How do I configure Sendmail or procmail to return large emails to the sender?

We have a client who lives overseas, and because he's in a slightly backwater area, he has very expensive internet. He said it costs him $7/Mb to use the internet. That's expensive! He would like us to be able to return to sender messages that are over 1MB with a note explaining about the issue.

I know that procmail would allow me to filter it. In fact right now, I've got a primitive filter up (I think)

MAILDIR=$HOME/Maildir

# accept small files
:0:
* < 1048576
$MAILDIR

# divert large files
:0:
* > 1048575
$HOME/largefiles # that's a folder I created

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This way his emails are just straight up lost. We could go through them later manually, but as I understand, procmail can't really send a message back to the sender.

I also understand that I could configure Sendmail to reject them for a certain file size

MaxMessageSize=1048576

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- but what I need to know is is it possible to limit this by the user?

Sorry if this seems obvious. I'm a little bit of a noob.

 

I may have found something. I found a procmail recipe online that would return the mail to the sender based on a specific email address. I've posted it below with a replacement of the criteria - making it the file size.

Now, I've read that this is dangerous because it can cause accidental spam propagation, but what I need to know is if I put this in the user's ~/.procmailrc instead of the global /etc/procmailrc (which calls spamassassin btw), would I be avoiding the problem, since the user-specific ("local") rc file is run after the global one, which would mean that it's running after spamassassin?

Thanks in advance.

Here's the script I think I would implement:

:0:
* > 1048575
| ( formail -rI"From: Automated Response <no-reply@domain.com>"; \
     echo "Email file size exceeded. This user has requested not to receive" \
     echo " messages over 1Mb in size." \
   ) | $SENDMAIL -oi -t

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