The maximum file size that Symantec Messaging Gateway (SMG) can accept does not meet the needs of the environment.
 

To adjust the message size, please perform the following procedure in the Messaging Gateway Control Center.

1. Click Administration.
2. Click Configuration (under Hosts).
3. Edit the host (scanner) for which you wish to make this change.
4. Click the SMTP tab.
5. Click Advanced Settings.
6. Adjust the Maximum message size in bytes limit field under the Inbound SMTP configuration Screen and then Outbound SMTP Configuration screen.
7. Click Continue.
8. Click Save.

Technical Information
NOTE: The message size is the body of the message plus attachment(s).

Encoding Overhead
When setting limits in the Maximum message size in bytes field, please be aware that MIME encoding overhead on your mail client adds approximately 30% to the file size of an attachment in a message, depending on the type of attachment.
E.g. if the attachment is plain text, hardly any overhead is added, whereas if your attachment is a .zip or .exe file, the overhead can be even more than 30%.
Also, Base64 encoding can add the same overhead (30% or more) to messages that only contain text in the message body.

Therefore if you want to send/receive attachments that are 6MB in size or smaller, you would need to set a 10000000 byte (10MB) limit in this configuration option.
If you want to send/receive attachments that are 10MB in size or smaller, you would need to set a 14000000 byte (14MB) limit in this configuration option.

Compressed files
The size limits apply to the size of the compressed file.
E.g.: If the decompressed size is over 10MB the mail will be accepted as long as the combined size of the compressed attachment, the message body, and the Encoding Overhead is less than 10 MB.