Exim>=4.94 transports: tainted not permitted

Title: Exim>=4.94 transports: tainted not permitted
Author: Fabian Groffen <grobian@gentoo.org>
Posted: 2021-05-04
Revision: 1
News-Item-Format: 2.0
Display-If-Installed: mail-mta/exim

The Message Transfer Agent Exim disallows tainted variables in transport
configurations since version 4.94.  Existing exim.conf configurations
in /etc/exim need to be reviewed for breakage prior to upgrading to
 >=mail-mta/exim-4.94 to avoid error conditions at runtime.

Since the release of Exim-4.94, transports refuse to use tainted data in
constructing a delivery location.  If you use this in your transports,
your configuration will break, causing errors and possible downtime.

Particularly, the use of $local_part in any transport, should likely be
updated with $local_part_data.  Check your local_delivery transport,
which historically used $local_part.

Unfortunately there is not much documentation on "tainted" data for
Exim[1], and to resolve this, non-official sources need to be used, such
as [2] and [3].

[1] https://lists.exim.org/lurker/message/20201109.222746.24ea3904.en.html
[2] https://mox.sh/sysadmin/tainted-filename-errors-in-exim-4.94/
[3] https://jimbobmcgee.wordpress.com/2020/07/29/de-tainting-exim-configuration-variables/