Mass Stripping Attachments by Directory, Age, Size

[Joseph Tam]

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 at gmail.com>