Hi Rachel,
You could accomplish the requirement using Content Filter if only you are currently limiting the actual sending size using a Content Filter in the ESA.
For example:
If currenty Exchange allows maximum outgoing mail size at 30MB and the outgoing Mail Flow Policy also allows 30MB, automatically ESA will accept this and proceed with filtering before sending the mail out. At the same time, if you are using a Content Filter to limit mail size larger than 15MB for all users, any mail larger than 15MB will be applied with an action (drop/bounce/etc.) If these small group of users are allowed to send email with maximum size of 25MB. You will need to create a new Outgoing Mail Polilcy with the members of the group listed as sender, then create a new Content Filter to detect maximum mail size of 25MB then apply an action without applying the other filter that detect 15MB for all other users.
You could also accomplish this if you could place the group to send from different mail server other than the one currently used by all other users. You need to create a new outgoing Mail Flow Policy with the new maximum mail size and apply to the new Sender Group with the new server IP or hostname listed, and place it on the top of the Sender Group order. For example, if the Exchange allows 30MB of maximum mail size and the new Mail Flow Policy only allows 25MB, and anything larger than 25MB for these users will be rejected. Keep in mind that the actual length of MIME-compliant base64-encoded binary data is usually about 137% of the original data length
Read: https://ironport.custhelp.com/app/answers/detail/a_id/1557
It will be more efficient if such control can be done from the Exchange rather than in the ESA.
Hope this helps.
Regards,
Donny
