Hi there!
I have found this in my server logs after trying to send VERY large file using the LAN mail:
Jun 11 09:35:39 icsserver.loc postfix/postdrop[2839]: warning: uid=0: File too large
Jun 11 09:35:40 icsserver.loc postfix/sendmail[2837]: fatal: root(0): message file too big
Fix is easy. Set unlimited attachment size. How?
Gain root and run those commands:
postconf -e mailbox_size_limit=0
postconf -e message_size_limit=0
and then restart postfix with this command:
systemctl restart postfix
Cheers.
Andrzej