To rephrase the title: If someone is trying to send an e-mail to individuals, they should only be able to select 25, however, if they are trying to send to an internal group, they should be able to send it to everyone in that group (not limited to 25). -- From Technet's articles, I was able to find a way to limit the number of recipients, but it interfered when someone was sending to a group.

Hi, Exchange can limit the number of receipt at five levels: 1. Restrict the number of recipients per message for the entire Exchange organization Note: You can't use the EMC to perform this task. 2. Restrict the number of recipients per message on a Receive connector Note: You can't use the EMC to perform this task. 3. Restrict the number of recipients per message on a transport server Note: You can't use the EMC to perform this task. 4. Restrict the number of recipients per message for a mailbox Note: You can perform this task with both EMC and EMS 5. Active Directory also has a global limit for the maximum number of recipients per message More information: Restrict the Number of Recipients per Message Exchange 2003 treats each member of an expanded distribution list as one recipient. Exchange 2010 treats a distribution group as one recipient. More information: Differences in Message Size Limits Between Exchange 2003 and Exchange 2010 Because you have restricted the recipients per message as 25. Now you need to create a distribution group, and restrict the sender who are allowed to send message to the distribution group. How to Restrict a Distribution List in Exchange Server 2010 Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.