Exim4 mail sending issue

Hello. The mail system doesn’t seem to work out of the box.

The issue is very similar to SMTP error 421 failed to add recipient. The webmail fails to send with the “SMTP error 421 failed to add recipient” error. And exim4 logs also contain “Taint mismatch, string_vformat: lsearch_open 35” which does not clarify anything.

Ubuntu 20.04 LTS
exim4 version 4.93, the latest available for it

There seems to be a similar bug in exim4, but it only should affect the 4.94 version.

After just a week of digging, I found a solution. There are two files present in /etc/exim4/domains/ config directory.

One is ip which contains the external IP of a server. It causes Taint mismatch, string_vformat: expand_string_internal 5016 error.
The other is fwd_only which appears to be empty. It causes Taint mismatch, string_vformat: lsearch_open 35 error.

When they are removed, the mail system starts to work as intended. I am not sure what causes this behavior.

You can replace:




However I find it strange as I haven’t had any issues with it in the past