Increase maximum message size

[rocklee44]

Hi all,

This is my environment : Exchange server 2013 CU19 + Fortimail 400E Firmware version : v5.3,build653,180328 (5.3.12 GA)  operates as gateway mode

Outgoing messages : from Exchange server go straight to internet not via Fortimail

Incoming messages : are scanned by Fortimail before come to Exchange server

I want to increase maximum message size from 10MB (default) to 20MB, I followed document to edit Mail Settings --> Domains and Profile session but it doesn't work.

Incoming messages larger then 10MB are rejected "The response from the remote server was:

552 5.2.3 Message size (20611500) is over limit (10485760)

"

What should I do ? Please give me some advices , thank you very much.

I'm sorry, I tried to upload images but it doesn't show up, I will try again.

[Carl_Windsor_FTNT]

In summary, Exchange to Exchange SMTP uses a different format to Internet SMTP and has to be re-encoded which changes the email size.  Check the link @Abelio linked, particularly the line:

The common Base64 encoding adds about 37% to the original file size, meaning that an original 20MB file could exceed a 25MB file attachment limit.

15MB + 37% = 20.55MB

Hence a 15MB exchange email would be blocked by a FML with a 20MB limit as FortiMail uses the absolute size including any encoding overheads.  Take this into account when setting your limits.

[Bromont_FTNT]

Jack, 

    When you attach a binary file to an e-mail the e-mail client converts binary to ascii so there's roughly 30% increase in size which is why you need to set the size limit on the Fortimail higher than the desired file size. See the link from abelio for further details.