Originally Posted by mmorse
So, you might to set zimbraFileUploadMaxSize 10-30% > than your attachment.
Also as a general rule, I set zimbraMtaMaxMessageSize 10% larger than the zimbraFileUploadMaxSize.
If I understand this right...say both are set to 10MB (and you tell everyone they can send 10MB attachments):
An email with a 9MB attachment and 100KB message body text. The attachment may be less than the 10MB zimbraFileUploadMaxSize, and so it'll get accepted by the file upload system. But when it's converted into a MIME message it ends up base64-encoded. Then add 100K of regular body text, and the resulting message (say 10.3MB or so) is then handed off to postfix, which checks zimbraMtaMaxMessageSize and promptly rejects the message if it's over the limit of 10MB.
Of course that would mean that you would set zimbraMtaMaxMessageSize even larger if you want to allow emails with multiple large attachments.