To allow larger attachments in Microsoft Exchange 2010, you may need to raise the message size limit in several places. A lower limit at any one of them will still block the message, so check each of these in the Exchange Management Console.
1. Organization Transport Settings
Organization Configuration > Hub Transport > Global Settings tab > Transport Settings
2. Receive Connectors
Server Configuration > Hub Transport > select a Hub Transport server > Receive Connectors > select a connector > Properties
3. Send Connectors
Organization Configuration > Hub Transport > Send Connectors > select a connector > Properties
4. Individual Mailboxes
Recipient Configuration > Mailbox > select a mailbox > Properties > Mail Flow Settings > Message Size Restrictions
5. Distribution Groups
Recipient Configuration > Distribution Group > select a group > Properties > Mail Flow Settings > Message Size Restrictions
6. Global Settings in ADSI Edit
Use ADSI Edit to connect to the Configuration container, then go to Configuration > Services > Microsoft Exchange > YourOrgName > Global Settings > Message Delivery > Properties and check these values:
delivContentLengthsubmissionContentLengthmsExchRecipLimit
7. Transport Rules
Organization Configuration > Hub Transport > Transport Rules. Check for any rule that restricts attachment or message size.
Related Microsoft article: Mailbox Size Limits Are Not Enforced in a Reasonable Period of Time. See also enabling an internal SMTP relay in Exchange 2010.
