https://bugs.exim.org/show_bug.cgi?id=2250
--- Comment #2 from David Carter <dpc22@???> ---
> I can see a steady stream of 'NULL character' error messages
> which appear to relate to remote hosts attempting to talk gibberish
> (TLS perhaps?) on port 25
Yes, we still see this now that I reverted to 4.89.1 (+security patch).
However NULL characters appearing spuriously in the middle of genuine SMTP
commands, for example.
2018-03-06 09:44:43 +0000 SMTP syntax error in "RCP? TO:<XXXXX@???>"
H=lists-4.csi.cam.ac.uk [131.111.8.103]:57345 I=[131.111.8.137]:25 NULL
character(s) present (shown as '?')
only happens when I am running 4.90.1.
Just to add:
After a single "RCPT TO" is rejected with one of these
501 NULL characters are not allowed in SMTP commands
errors, further recipients on the same SMTP transaction work just fine.
I can't immediately find evidence of two separate "NULL characters" errors on a
single SMTP transaction. However Mailman is capped at 500 recipients per
message. After that point it breaks things up into multiple messages.
Our mailing lists system has been running Exim 4.89 throughout: only the
receiving end has changed.
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