Hi Matthias,
Thank you for responsibly asking reasonable
questions.
My humble comments follow yours, below....
On 11/30/2025 11:03, Matthias Andree wrote:
> Am 30.11.25 um 10:00 schrieb Kingsley G. Morse Jr.:
> > Package: fetchmail
> > Version: 6.6.1-1
> > Severity: normal
> >
> > Hi Laszlo,
> >
> > Thanks for maintaining fetchmail.
> >
> > I run it many times every day.
> >
> > The main reason I'm writing is to share how I
> > stopped repeated bounce messages from exim4 by
> > changing fetchmail's default configuration.
> >
> > The immediate symptom was a company hosting a POP3
> > account complained that I was sending too many
> > emails.
> >
> > exim4 kept sending bounce messages when fetchmail
> > tried to deliver an email with a line longer than
> > allowed by RFC 5322 2.1.1.
> >
> > I think the reason why exim4 sent multiple bounce
> > messages was fetchmail
> >
> > left the offending email in the POP3 account
> > and
> >
> > asked exim4 to deliver it again, each time
> > fetchmail was run.
> >
> > fetchmail has the option "set no softbounce".
> >
> > But Debian's default configuration doesn't use it.
> >
> > fetchmail's man page describes
> >
> > "set no softbounce"
> >
> > as
> >
> > "Delete permanently undeliverable mail. It is
> > recommended to use this option if the
> > configuration has been thoroughly tested."
> >
> > I
> >
> > added "set no softbounce" to fetchmail's
> > configuration and
> >
> > restarted my fetchmail daemon.
> >
> > I saw 2 spams with lines longer than allowed by
> > RFC 5322 2.1.1 since then.
> >
> > It seems to me that both were handled better.
> >
> > a.) They were properly deleted from my POP3 inbox
> > after the first time exim4 rejected them and
> >
> > b.) only one line in exim4's log file looks like a
> > bounce.
> >
> > In the interest of being complete and accurate, I
> > also upgraded my version of fetchmail from 6.5.6-1
> > to 6.6.1-1.
> >
> > However, fecthmail's man page for "set no
> > softbounce" suggests to me that it's a more likely
> > explanation for the fix.
>
> Did you use daemon mode?
Yes.
> Can you provide the fetchmail log including the bounce before and after your
> configuration change?
Unfortunately, no.
> I would like to see if there's a bug lingering somewhere in the "softbounce"
> logic. The main purpose is "don't delete mail", so if we leave the message
> on the server for later reattempts, we shouldn't send bounce mail.
I agree bounce messages shouldn't be sent while
mail is kept on the server for later reattempts.
It seems to me that a complication is it's not
fetchmail sending bounce messages.
It's exim4.
My understanding is Debian's default configuration
is in the file named
/etc/exim4/exim4.conf.template
under
acl_check_data:
It says to "deny" mail with lines longer than 998
octets ( as required by RFC 5322 2.1.1 ).
For your convenience, I left a test email in .eml
format that
has a long line
wasn't deleted at my POP3 mail server and
led to multiple bounce messages being sent
at
http://loaner.com/test_mail.eml
Maybe you could use it to
replicate the bounces and
look for a lingering bug somewhere in the "softbounce"
logic.
Feel free to let me know if you happen to have any
questions or concerns.
Thanks,
Kingsley
--
Time is the fire in which we all burn.
