It's important to know if a tenant has any very large distribution lists as these might be the source of reply-all mail storms. An old article explains how to report the membership counts for distribution lists.
The New-DistrubtionGroup cmdlet has been in Exchange since 2006. It creates a new distribution list that is easily populated with a few commands.
How group metrics and MailTips work to warn users when they are composing an email message to a large number of recipients.
How to use PowerShell to report the member counts for distribution groups in an Exchange Server environment.
A look at some of the pros and cons of using separate security and distribution groups in an Exchange Server environment.
How to configure Exchange Server 2010 to allow non-administrators to manage distribution group membership requests.
How to use PowerShell to find all Exchange Server distribution groups that are managed by a particular user.
How to remove a user or group from the list of authorized senders for an Exchange Server distribution group.
How to grant a user or group permissions to send as an Exchange Server 2010 distribution group.
How to use the Exchange Server 2010 management shell to list who can send to restricted distribution groups in the organization.
How to grant a user permissions to send email on behalf of an Exchange Server 2010 distribution group.
Exchange Server 2010 allows you to restrict who can send to distribution groups, but it is important to understand the pros and cons of each way it can be done.