Increasing Attachment Size in Posfix Rumi, July 19, 2019 Postfix by default restrict attachment size to approx 10MB i.e. 10240000 bytes. You can check 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, you need to change postfix attachment size only. I spent half-hour debugging dovecot to increase attachment size, just to realize that above change in postfix config was all I needed! Administrations Configurations (Linux) Postfix