2023-07-17    EXIM SYSADMINS BEWARE, DEBIAN BOOKWORM IS A
                              MAJOR UPDATE

A warning for all sysadmin using Exim on Debian Bullseye, don't switch
to Debian Bookworm just yet.

The changelog will tell you that, for Exim 4.96-15 in Debian Bookworm:

,----
| The allow_insecure_tainted_data main config option and the "taint"
| log_selector were removed
`----

However, if you run Debian Bullseye, you never get the warning. Those
might have come with Exim in unstable/bullseye-backports:

,----
| Please consider exim 4.93/4.94 a *major* exim upgrade. It introduces the
| concept of tainted data read from untrusted sources, like e.g. message
| sender or recipient. This tainted data (e.g. $local_part or $domain)
| cannot be used among other things as a file or directory name or command
| name.
`----


,----
| This WILL BREAK configurations which are not updated accordingly.
`----

That version at least came with a quick fix:

,----
| .ifdef _OPT_MAIN_ALLOW_INSECURE_TAINTED_DATA
|  allow_insecure_tainted_data = yes
| .endif
`----

Which is not available in Bookworm.