Fetchmail bouncing
I recently got informed that a large e-mail kept getting bounced by my mail server. A little investigation showed that by default the postfix program limits mail to 10MB.
This can be upped to 100MB with this command:
postconf -e 'message_size_limit = 104857600'
In addition, if like me you have your mail being retrieved from an external mailbox with the fetchmail then you may want to configure the "--nobounce" option in your startup script (/etc/init.d/fetchmail on some systems). This should send a bounce e-mail forward, but not back to the sender. Not that I've tried sending a 100MB e-mail to test this.