On Thu, 18 Mar 2021, Plutocrat wrote:
I've been looking around for a solution to this problem. I want to prune down the attachments on a server before a migration. Some of the emails are 7 years old and have 40Mb attachments, so this seems like a good opportunity to rationalize things. So perhaps I'd like to "Remove all attachments from emails older than 2 years, in the .Sent directory", or "Attachments over 10Mb anywhere in the mail tree"
I've found the strip_attachments.pl script here <https://fossies.org/linux/Mail-Box/examples/strip-attachments.pl> which works fine on mbox (as tested on my local Thunderbird mboxes), but not on maildir which is on the dovecot server. My Perl isn't strong enough to re-purpose it.
It you have anything that works on mbox, it will probably work on Maildir as each file can be considered a single message mbox. You can combine the script with
find ~user/MailDir -type f ... -exec /path/to/mbox-strip {} \;The ... can be replaced with more file tests (like minimum size or age or only within */cur/) to cut down on processing.
I wrote a gawk script to slim down a multi-Gb Outlook mbox for a user, but it wasn't really complicated, just matching for /^Content-Transfer-Encoding:.*base64/i header (virtually all bulky data will be encoded this way), buffering the base64 data part, then outputting it if it was small, or deleting/replacing/extracting it otherwise.
It was a one-off discarded tool but I can hunt for it if you're hard up.
I've looked at ripmime and mpack/munpack, and although they seem like useful tools to do the job of deconstructing the mail into its constituent parts, it doesn't seem to help in re-building the email. I think they could be used with a bit of study into mail MIME structure, and used with a helper script.
So before I take a deep dive into scripting my own solution, I just wanted to check if anyone else on the list has been through this and has some resources or pointers they can share, or maybe even someone to tell me "Duh, you can do it with doveadm of course".
MIMEDefang may help.
Joseph Tam <jtam.home@gmail.com>