MAILATTACH

This program starts a process which listens on the LOOPBACKv4 address for
incoming connections from postfix. The postfix master should view this as an
advanced filter as explained in their documentation for post queue filtering:

http://www.postfix.org/FILTER_README.html

The original attempt was to implement this as a pre queue filter, but this
required the milter protocol and postfix currently does not implement the
replace body function from libmilter.

You can specify the following command line options:

--abort-pgp --noabort-pgp
	To either abort the attachment process if PGP encryption or signatures 
	have been detected or not. If true, the mail will not be modified.

--abort-dkim --noabort-dkim
	To either abort the attachment process if DKIM signatures have been
	detected or not. If true, the mail will not be modified.

--in-port -i
	The incoming smtp port/the port from which mail is received. Defaults to
	4269.

--out-port -o
	The outgoing smtp port/the port to which mail ist passed through.
	Defaults 4270

--directory -d
	The directory inside of which the attachments will be stored in. Please
	DON'T specify a / at the end!

--url -u
	The base which should point to the same location as the directory does,
	for exaple if the directory is /var/www/html and the URL base is 
	https://example.com then a file in /var/www/html/attachment01.pdf should
	be linkable via https://example.com/attachment01.pdf
	Ah and please, please, pretty please disable directory indexing on your
	webserver! 
	That WILL BE a security riks!
	Please don't specify a / at the end, and have the URL encoded!

--other-base64 --only-base64
	Decides wether ONLY base64 encoded files should be removed from the
	actual mail, or ALL files.

--minfilesize -s
	The minimum file size which a file has to have before beeing attached.
	Thissize is before base64 decoding if nescessary. Size is in bytes,
	ONLY bytes. Do NOT prefix a M or K, it will not be parsed! Defaults to
	500Kb. If 0 is specified, all files will be attached. A negative value
	effectively disables us.

HOWTO

We essentially are MITM sniffing your email traffic and playing proxy from your
postfix to your postfix. That's how this is intended to work according to the
postfix website.

This program needs to be started via it's own systemd service on system boot.
You need to add the in and oputput ports to your postfix queue as described in
the link above. For example, a setup with the default values looks like this:
|-------|    SMTP    |-----------|  SMTP    |-------|
|POSTFIX|     -->    | MAILATTACH|   -->    |POSTFIX|
|-------|  n    4269 |-----------| n   4270 |-------|
                         |
                         |
                         v
		     |-----------|
                     |Attachments|
		     |-----------|

DIRECTORY CLEANING

If you want to regularly purge old files from the directory, you can start the
shell script clean.sh in this repository via a chron job. It will by default
remove all files older than 10 days. If you want to write your own shell script
or let something else do the job for you, the directories where files are stored
are structured like this:
2020-01-01T1430-3893482323323
^DATE     ^TIME^RANDOM NUMBER

The random number at the end consists of several signed integers, therefore it
sometimes has one or more - in it.