Attachment size limitations
From Qmailtoaster
Attachment size limitations
The default setting for 'databytes' is 20971520 which is a sane, default number. But MIME overhead is fairly high, so that 20m limit means you may not be able to receive attachments larger that 12-15m. That may seem to not be a problem, but if you host a domain that deals in large attachments for data transfer, you may need to increase that number in /var/qmail/control/databytes. You could set that to 0 (not advisable) to accept attachments regardless of size, or figure out what is the largest attachment you will recieve, then double that in the databytes file. Yes, ftp would be a better answer for moving that chunk of data around. Do you really want to have to talk the sender through a filezilla download, install, configure, connect, and upload, or worse, a command session? Point is that email is more widely known than the venerable ftp, and most everybody has an email client already installed and knows how to use it.