The default maximum attachment size limit on a new Postfix installation is 10 MB.
By 2011 standards that’s probably still okay. But as of 2021 users expect to be able to send large attachments. One could get into an argument with users about the mess a mail server gets into if extremely large attachments are sent, or one could just raise the limit.
/etc/postfix/main.conf has this line or none (the default size limit)
Our recommendation for the year 2021 is to up it a bit. When this article was written, Google had a 25 MB limit, and Office 365 had a configurable 1 to 150 MB limit.
For the purpose of this article we will use use 50 MB which still seems fairly sensible.
Once you have made the change, and reload the Postfix configuration, use the following command line to see if it worked:
# postconf | grep message_size_limit message_size_limit = 51200000