Exchange Server 2013 CU1 or later (not RTM) supports co-existence with the following previous versions of Exchange Server:

  • Exchange Server 2010 SP3
  • Exchange Server 2007 SP3 + update rollup 10

There will be no co-existence support for Exchange Server 2003. If you’re still running Exchange 2003 and are looking to upgrade to Exchange 2013 you’ll need to do an interim upgrade to Exchange 2010 (or 2007) first. I recommend an upgrade to Exchange 2010 instead of 2007, as it makes for a better upgrade experience to Exchange 2013.

Active Directory Requirements for Exchange Server 2013

Exchange 2013  support a Windows Server 2003 Forest/Domain functional level, and Windows Server 2003 SP2 domain controllers.

A schema update will be required as usual, and this is part of the same service pack/update rollup that is required for co-existence support.

The Upgrade Process for Exchange Server 2013

The high level documentation and general guidance for Exchange 2013 upgrades has been published at the Microsoft Exchange Server Deployment Assistant.

For more detail on the Exchange 2013 upgrade process you can follow my article series here:

Many of the challenges in these upgrades come not from Exchange itself, but more from the integration points such as third party software. In that respect you will need to watch for announcements from the vendors for products such as your backup software.

Client Support for Exchange Server 2013

The following clients are compatible with Exchange Server 2013.

For more information on discovery of client versions in your environment see the following article:

There is no support for Outlook 2003. If you’re still running Office 2003 in your environment and intend to upgrade to Exchange 2013 then you will need to upgrade Office first.

About the Author

Paul Cunningham

Paul is a former Microsoft MVP for Office Apps and Services. He works as a consultant, writer, and trainer specializing in Office 365 and Exchange Server. Paul no longer writes for


  1. kamran

    Hi ,

    i have migrated to 2013 from 2010 .

    there is an automated email generated from the system to group emails , the emails are receiving to all users inside the distribution group email but there is more groups/user within that email group who are not recieving the emails.

    for Example , is group email address that has 3 users and one more distribution group added.

    3 users within recieving the email but other group users are not.

    1. Avatar photo
      Paul Cunningham

      You should start investigating by running message tracking log searches using PowerShell.

  2. Victor

    Thanks a lot!

  3. Victor

    I had great success using your guides in a migration from ex2003 to 2010, now o need to upgrade ex2007 to 2013, single forest, with single org on single server, but want to know which ones of your published guides will fit my needs better, in order to buy them

    Thanks in advance for your help

    1. Avatar photo
      Paul Cunningham

      I don’t have a 2007 -> 2013 specific guide. You can go to the Exchange Deployment Assistant at Microsoft and it will generate some guidance for you.

      1. Victor

        Well, i am already digging in the “Deployment Assistant at Microsoft” and it has basically the big milestones, is the process more like 2010->2013 or more like 2007 -> 2010?, thank you

  4. Sam


    The scenario is we acquired one portion of the company and we created new mailboxes for the new users whoever coming to our company. Now those users are having outlook contacts. can you tell which one is best approach to migrate user contacts from their old company outlook to new company outlook. We were thinking to export the contact and import manually. Is there any other efficient way for this contacts migration from old company to new company?

  5. MAu Flores

    Hi Paul, I beleive you wrote your Migration Guide 2010-2013 in 2013 year. I am interested in buying it, but I have some doubts …

    At this moment your guide is updated considering Exchange 2013 SP1 CU13?

    With CU13 there is a new concideraciones to keep in mind?


  6. Patrick

    Hi Paul,

    I’ve searched many different places and can’t seem to find the answer to my question about certificates as it pertains to a 2007 to 2013 upgrade. We have a 2007 CAS and we are ready to introduce our 2013 mailbox and CAS into the environment. We are using a wildcard cert on the 2007 CAS. Could I simply export that along with the private key and import it in our 2013 CAS?

    If so, the process as I see it is:
    1) install 2013 Mailbox and CAS into environment
    2) import wildcard cert onto 2013 CAS
    3) change webmail.domain.local and autodiscover.domain.local internally to point to 2013 and create legacy.domain.local to point to 2007.
    4) run the following scripts to fix having a split DNS environment:

    Set-ClientAccessServer -Identity servername -AutodiscoverServiceInternalUri

    Set-WebServicesVirtualDirectory -Identity “internalservernameEWS (Default Web Site)” -InternalUrl

    Set-OABVirtualDirectory -Identity “internalservernameoab (Default Web Site)” -InternalUrl

    5) redirect external requests for webmail in firewall to flow to 2013 CAS instead of 2007. Create A record for legacy externally and have it flow through firewall to 2007 CAS.

    6) Pray.

    1. Avatar photo
      Paul Cunningham

      As long as the wildcard certificate is valid for your namespaces. But you’re mixing domain.local and in your examples there so I can’t really tell what namespace you’re actually trying to deploy.

      What you’ve spelled out is not the entirety of the co-existence and migration process. The Exchange Deployment Assistant would be a good place to go and find out more for that scenario.

      1. Patrick

        Hi Paul,

        We have an internal AD domain that ends in .local and externally people would obviously use the .com which is why they are mixed. Currently, it is impossible to get a certificate referencing a .local so I’ve had to use a workaround for the internal network while still making sure the external clients can connect without a problem. Thanks for the info, I’ll check out the Deployment Assistant.

          1. Patrick

            Thank you, Paul. You’ve just cleared up a huge sticking point involving .local addresses and certs that I wasn’t able to find anywhere else on the Internet. I have one more question and then I won’t bother you with this upgrade any more.
            In all the documentation I see, it says to point away from the 2007 CAS to the 2013 CAS. We are not using that URL, instead we are using Instead of bothering with creating for the 2007 CAS, can I simply create a new record for and leave the for the 2007 environment? I’m thinking that will cause less interruption for the end users and allow for a smoother transition.


          2. Avatar photo
            Paul Cunningham

            Any document you’re reading will be using example namespaces. You need to interpret the advice in the context of your own environment.

            What they are saying is:
            – move the OWA namespace to 2013
            – establish a new “legacy” namespace (you can call it anything you like, “legacy” is just the example) that points to 2007 (the 2007 server then also needs a new SSL cert that includes that name).

            There’s additional config steps as well, no doubt you’ve got those in your Exchange Deployment Assistant instructions already, I’m just giving you the high level.

            When users login via the 2013 OWA interface, they are redirected to the “legacy” namespace if their mailbox is still on 2007.

            The outcome is that nobody needs to learn a new OWA URL, you get to keep the existing one, and 2013 will connect or redirect 2007 users as required during the co-existence phase of your deployment.

  7. Aravind

    Hi Paul,

    Currently we are under progress of Co-Existence migration from Exchange 2010 to Exchange 2013.

    Is Exchange 2010 SP3 ( supported for Exchange 2013 CU10 (15.0.1130.7) for Co-Existence Migration.

    Please help me out.


  8. Giovanni

    Hi Paul,
    I’m migrating from an E2007 Sp3 RU 15 on Windows 2003 to E2013 Sp1 CU8.

    I configured (and triple checked) all virtual dir an authentication settings on both platform following the best practices especially for externalURL and IIS Authentication (NTLM, Base).

    Despite this, OA on E2013 is not proxied to CAS2007: I receive an error trying to access a legacy E2007 Mailbox using CAS2013 as endpoint.

    OWA redirection (legacy) works fine for both E2013 and E2007 mailboxes. It looks there is an issue in proxying authentication from CAS2013 to CAS2007.

    Have you ever experienced something like this? Any help or pointer would be VERY appreciated…
    Thank you.

    1. Avatar photo
      Paul Cunningham

      Should you run it? Read the scenario they spell out. Does it apply to your environment? Have you walked through the steps they demonstrate to see if your environment matches with the example in the article?

      I know you’re looking for a yes/no answer, but I have no visibility of your environment or the problem you’re experiencing. So this is an analysis you need to do based on the detailed article Microsoft has published.

  9. Dave

    Hi Paul,

    After implementing co-existence, would you expect Exchange 2007 to become slower to respond to Outlook clients? We have an extremely large public folder database. Tens of thousands of folders and millions of email messages. I only have about 40 of the 380 employee mailboxes moved to 2013 but we’ve had a lot of reports lately about public folders being slow to respond. I’ve looked at perfmon counters and everything there seems normal. I was wondering if it had something to do with proxying via Outlook Anywhere to 2007 instead of MAPI causing overhead. Your thoughts?

    1. Avatar photo
      Paul Cunningham

      No I would not expect them to be slower. The timing may just be a coincidence. You also don’t say whether the complaints are only coming from users who have been migrated.

      Performance complaints aren’t the sort of thing to just look at back end perf counters for. Hopefully you’ve gone out and looked at the user’s experience first hand.

      1. Dave

        Most of the 40 I’ve already migrated work in the office and are in cached mode, so the only time they’ll notice performance is when they’re accessing public folders. We have about 115 employees that work full time in Citrix so they’re Outlook is in online mode. Most, if not all, are still on Exchange 2007 so they’re accessing their mailbox and public folders directly from Exchange. Our employees access public folders a lot, and I believe it was most noticeable then. There would be times where they would click on a public folder and would have to wait 15-30 seconds or more and would get the famous Outlook pop-up box saying in the taskbar saying “please wait…..” It could be a coincidence but these reports starting coming shortly after we entered the co-existence phase. I’m not seeing any unusual errors in the event logs that would point to something being wrong, and the performance counters I’ve looked at on the Exchange 2007 mailbox seem good.

        I moved about 30 mailboxes last night for employees that work exclusively in Citrix. I will see if their mailbox access has improved today but that still won’t have an effect on their public folder access.

  10. Maurice

    Hi Paul

    I purchased your guide Exchange 2003 to 2010 nice and easy to read and implement. I’m now on another project where I need to migrate Exchange 2003 to Exchange 2013 using two forests. Is there a document around on how to set it up and to share the same name space while in transition and keeping GAL and Free/Busy in synch between the orgs.

    1. Avatar photo
      Paul Cunningham

      I don’t have one, but I’m sure there’s something out there. Probably a combination of TechNet and other websites found via Google search will give you enough info to get through it.

  11. Jeremy

    Hi Paul,

    Your articles have been a great help in our migration from 2007 to 2013. I have finished moving all users to 2013 and all mail is being routed through 2013 now. We’re at the point where we are ready to shut down the 2007 servers, and most guides go through the process of removing the 2007 databases and uninstalling Exchange 2007. My question is, is this really necessary if everything works as expected after shutting down the 2007 servers? Is it like AD where the 2007 servers need to be removed from the environment similar to a domain controller, or do I need plan on booting back up the 2007 servers after having them shut off for a week to verify everything still works – just to uninstall 2007?

    Thanks for your help.

      1. Jeremy

        I appreciate the response. I’ll plan on doing that…going to have to figure out how to remove the public folder database first though. Currently getting “the public folder database contains folder replicas” error, even though I’ve already removed all public folders. I’ll try a few things to get rid of that database today.

        1. Jeremy

          In case anyone else has this trouble, I got to where Exchange 2007 would try to delete the public folder database, but it would fail with this error: Object is read only because it was created by a future version of Exchange. I saw you had an article on this related to Exchange 2010 but the remove-publicfolderdatabase command isn’t present in 2013.

          This update to 2007 fixed it and let me remove the public folder database.

  12. Luke C.

    Hello All,

    I have been tasked with an EX2010 to EX2013 migration. I have one EX2010 server (60 mailboxes) on server 2008 r2 and plan on installing EX2013 on server 2012 r2. When I install EX2013 will it interfere with my EX2010 server in any way? Will mail flow normally until I start migrating mailboxes.


    1. Avatar photo
      Paul Cunningham

      Hi Luke, why not read through the article series on migrating from 2010 to 2013, and you’ll learn how the process works and which stages have user impacting changes (and how to avoid problems).

  13. Derli Campos

    Hello all,

    I have managed to install Exchange 2013 as an upgrade of Exchange 2007, everything worked fine on the migration part.

    Today, I decided to decommission Exchange 2007 as it is no longer necessary to keep on the domain, but I first powered it down to see how everything behaves.

    For my surprise Exchange 2013 has not been able to receive external e-mails, so I had to bring Exchange 2007 back online and the e-mails started to come naturally.

    Any idea on where to start?

    Derli Campos

    1. Avatar photo
      Paul Cunningham

      Sounds like you haven’t updated your firewall to direct incoming SMTP connections to Exchange 2013.

  14. Gerald Hollins

    I wish 2013 had a separate Information Store for each Database

    1. Avatar photo
      Paul Cunningham

      What do you mean? One of the improvements in Exchange 2013 was a separate worker process for each database instance.

  15. Kush

    Hi Paul,

    I am in the process of planning an upgrade of Exchange 2010 to Exchange 2013. Would you happen to have some step by step instructions on how to start off running EX2013 in Coexistence and then eventually migrating everything over from EX2010 to EX2013. Just as an FYI we currently have 2 DAGs configured in our environment.

    I am hoping you will be able to share some of our knowledge and recommend how I tackle the upgrade?

    Keep up the good work and hear from you soon.

  16. Michael G.

    I have a weird questions. We’re on exch 2010 and we purchased a smaller company on 2013. is it possible to migrate their 2013 mailboxes to our 2010 environment?

    1. Avatar photo
      Paul Cunningham

      I can’t be very specific on details, but there will no doubt be options ranging from establishing a Forest trust and doing a cross-org migration, or using third party tools to migrate with or without a trust (eg solutions such as Quest, MigrationWiz…)

  17. Dave Ainslie

    Hi Paul,

    I’ve come across this page and hoping you can help, i have upgraded from Exchange 2010 SP3 (Rollup5) on Server 2008 R2 to Exchange 2013 CU2 on Server 2012 & followed some online guides. Everything is working fine in co-existence, both exchange servers talk to each other and i can migrate (local move) mailboxes over from exchange 2010 to exchange 2013. The only problem i have is sending external email from exchange 2013. I have a 2010 edge transport server and i think it is something to do with the send connector on exchange 2013 not going through the edge? im stuck here because i dont want to move mailboxes and decommission the 2010 server until i can outbound external email from the 2013 server.

    Any Ideas what to check first?

    1. Dave Ainslie

      Notto worry i have got it working, turns out i just needed to add the new server to the internal server range on the edge server connector

  18. Carlo

    Hi Paul,

    Good Day!

    Just to share to everyone my environment, I have 2 Exchange Server configured DAG in place, Mailbox Database located in Main site and DR site is already replicating.
    Some queuing encountered during replication, But i think this is normal for total of 10 mailbox database replicating to DR site.
    I have some minor issue encountered. I have 13 users which failed during the migration process from Exchange 2007 to Exchange 2013.
    Can you please share your thoughts on how to resolve this kind of issue.
    I’ve tried to do these alternative steps to migrate.

    1. Export/Import the .pst file to local PC.- Client side

    Upon doing these steps in client side was successful, but when i go to the server-side in Exchange 2013 configuration i am lost on this part.

    Please share your thoughts 🙂

    Godspeed! 🙂

  19. Daniel

    Hi Paul,

    I have a ex 2010/hosting and I have to migrate it to a new exc 2013 forest. I followed this good article “” in a lab environment and I got success in a common 2010. When I deployed the hosting mode I got an error during the New Migration Endpoint. So I don’t have sure about if this issue is related to the /hosting or I am missing something. I did the trust, enable the MRSProxy, The “Prepare-moverequest worked fine, I export/import the certificates, but no way. This message shows up when asked to validate the FQDN of source domain:
    “Remote MRS proxy server:
    The FQDN of the Exchange server that the Mailbox Replication Service (MRS) Proxy is on. ”

    The connection to the server ‘’ could not be completed.
    Do you have any idea?


  20. Vishal

    Hi Paul,

    I am in the process of upgrade to Exchange 2013, my current setup is like, 2 Server 2012 DC, 4 Exchange 2010 SP3 (2 CAS + 2 MBX in DAG), 4 Exchange 2013 CU2 (2 CAS + 2 MBX in DAG). Users who are having there mailbox on 2013, they are able to access and other things fine without any issue, users who are having there mailbox on 2010, they are also able to access OWA and other things fine without any issue, but when I try to access 2010 user mailbox using 2013 OWA which is FE & Internet facing, I’ll get 2013 owa login page and once I entered the credentials, its giving me blank page, previously I was getting the error mentioned in the below TechNet article. I know its configuration and permissions issues on virtual directory and IIS

    Please help and if possible please share the configuration required for the proxy to work.


  21. John

    Hi guys,

    We are currently running exchange 2010 on a 2012 server. If we want to migrate to exchange 2013 do we need to purchase another server, or I can just install exchange 2013 on the same server as 2010 and then just move the roles and mailboxes?


    1. Avatar photo
      Paul Cunningham

      There’s no in place upgrade for Exchange. You’ll need a new server.

  22. David

    Hi Paul,
    I migrated from Exchange 2003 to Exchange 2010 about 20 months ago using your migration guide. I can’t thank you enough for writing it. Without it, I think I’d still be floundering in mixed mode. I’m now just taking my first look at Exchange 2013 and, of course, I’m looking for your Exchange 2010 to Exchange 2013 Migration Guide. Do you have an ETA for the guide, or even a ball park guess as to when it might be completed?

  23. Victor

    Hi paul i have a question about to upgrade Exchange 2010 with server 2008 r2 to Exchange 2013 Server with 2012, my server 2008 have exchange 2010 and have the Active Directory Domain Controller my question is after migrate exchange 2010 to 2013 do i need to migrate manually the ADDomain Controller to the server with 2012 or this process is made it automatic on the upgrade? because i need to format the server with 2008 r2. thanks

    1. Avatar photo
      Paul Cunningham

      A few points:

      1) Yes you would have to manually set up the new server as a DC. The Exchange migration won’t do that automatically for you.
      2) You must make the server a DC *before* Exchange is installed. You cannot promote/demote a server as a DC after Exchange is installed.
      3) Despite 1 and 2 you should not install Exchange on domain controllers. It is not best practice and I personally find it far more trouble than it is worth.

  24. Santhosh

    Could you please post the link for outlook 2007 & outlook 2010 updates which required for connecting to Exchange Server 2013?

  25. Victor

    i have a question: After upgrading to exchange 2013 what happens with Active Directory do i need to move it manualy to the new serve with Exchange 2013 or this is an automatic process? because after migration i want to format the “old server”. thanks

  26. ali

    hey Paul,
    Good day to you.. why you are quite on exchange 2013 migration.. i mean i was expecting a lot from you with my other friends.
    will you right a migration guide book on it ?

    1. Avatar photo
      Paul Cunningham

      It takes a long time to write books, and the Exchange 2013 migration process is still very new. Yes I am writing guides for it.

  27. Rajith

    Hi Camberton,

    The custom receive connector that you created in 2013, is it set to use the “Frontend transport” for the Role, rather than the default. This is required for a proper mail flow. The issue should be fixed in the coming rollups.


  28. Andrey

    Do not move to Exchange 2013 till service pack available. Receive connector is not operating properly. It’s nightmare! You must restart Transport service each 3-4 hours, because its freezing!!!!

    1. Erend

      Hi Andrey,

      Can you give us more details about it?


      1. camberton

        It’s true, if you want to use custom receive connector for example to receive mails from external, you get randomly “service unavailable”…

        The solution for me is to use the default connectors and delete my custom. The default connector is already configured for anonymous external mail receive.

        Moreover, mail flow as never used my custom connector, even if i disable anonymous on the default !! continue to use it even after restart service transport…

        I use CU1 and i’m waiting for SP.

        Question : I have also 2010 in hosted mode. Is it possible to integrate an Exchange 2013 ? is it mandatory to do cross forest migration ?

        Thx by advance.

  29. Sime

    Hi Paul

    I bought your guide “Exchange Server 2007 to 2010 Migration Guide” and it was great. Are you going to write “Exchange Server 2010 to 2013 Migration Guide”?

      1. Mohammed

        Hi Paul,

        Again at your doorstep. Need your help.

        Exchange 2013 certificate management is really headache and tricky.

        I have assigned POP services to the certificate but the customer does not want POP3 connection to be secure. Now I am not able to unassign the POP3 from the certificate.

        I tried a lot using EMS but invain.

        Need your help in this reagard.


        1. Avatar photo
          Paul Cunningham

          Exchange 2013 won’t allow you to remove an SSL certificate from a service that requires SSL. However you can replace the certificate with another one if you wish.

          See more here:

          But it sounds to me what you’re trying to do is allow unsecured logins for POP. You don’t need to remove or replace the SSL cert for that, you’d just need to change the POP login method on that server to one of the plain text options.

  30. Hi Paul,

    I have updated exchange 2010 SP3 and added exchange 2013 in a Lab Environment. Have successfully moved mailboxes from exchange 2010 SP3 to exchange 2013. But still i need your advice to do it for our production environment. Still CU1 is not released. Shall I go ahead for the migration of mailboxes without waiting for CU1 for exchange 2013.

    Also I need to know the significance of Cumulative Update 1 for exchange 2013.


    1. Avatar photo
      Paul Cunningham

      The significance of CU1 is that it is the supported version for co-existence with Exchange 2010 and 2007. Without CU1 you will be running an unsupported environment so obviously I do not recommend that.

      1. Ben

        Hi Paul

        Does CU1 still needed if we are going to upgrade from Exchange 2003/2010 to 2013 and remove previous version? (Not Co-existence)


        1. Avatar photo
          Paul Cunningham

          If you’re talking about the same AD Forest/Exchange org then there is no way to avoid co-existence, you will need to spend some time in co-existence while you’re migrating. CU1 is required for co-existence. Also Ex2013 can’t be installed in an org that has Ex2003 servers.

          If you’re talking about migrating to a new AD Forest/Exchange org then you can do that now, no need to wait for CU1 unless you want to wait for CU1 to deliver other bug fixes.

  31. Ryan

    Paul, Do you know if the new Update Rollup 9 for Exchange Server 2007 SP3 has the supported coexistence with Exchange 2013 built in? This was released mid to late Dec 2012.


    1. Avatar photo
      Paul Cunningham

      There’s no co-existence support yet in any of the 2007/2010 SP/UR releases.

      1. Thiago Silva


        Can you inform, when Microsoft will release for buy Microsoft Exchange 2013 ?


        Thiago S.

  32. Jean Maurice Prosper

    HI, I am running a hosted version of Exchange 2010 SP2, is there anyways to migrate to Exchange 2013 ? Is that at least supported or should I do a long process of new install and migrate the mailboxes manually etc ?



  33. Chris Brown

    Great article, Paul. I’m really looking forward to Exchange 2013 and the new possibilities it introduces.

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