Postfix by default restrict attachment size to approx 10MB i.e. 10240000
bytes. You can check attachment size it using following command: postconf | grep message_size_limit To change attachment size to say 50 MB, run a command like: postconf -e message_size_limit=52428800 Note: If you are running a mail server with SMTP/IMAP access on it, you
only need to change postfix attachment size setting. I spent 20 min.
debugging dovecot to increase attachment size, just to realize that above
change in postfix config was all that was needed!...