On 22/01/2024 17:16 EET Steve Dondley via dovecot <dovecot@dovecot.org> wrote:

...

there is no user in the above line

...

Some characteristics of the problem that may offer a clue:

• happening with multiple users, not just the same one
• happens from different IP addresses.

bots detected

The problem is happening to real users on real devices who are reporting very real connection errors, not bots.

...

...

• happens about 3 to 5 times per day and the errors come in batches like above
• MS Outlook error is:

why is it a microsoft problem now ?

...

reported error (0x80042109): ‘Outlook cannot conect to your outgoing SMTP email server. If you continue to receive this message….blah blah blah

disable pop3 in dovecot, problem is then gone

The same problem happens on IMAP. Example from log:

Jan 21 01:51:55 ip-172-30-0-131 dovecot: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=87.xxx.xxx.xxx, lip=172.30.0.131, TLS handshaking: read(size=598) failed: Connection reset by peer, session=<ctMkJm8PM9RX7LDO>

Hi!

Ensure your config says

auth_mechanisms = PLAIN LOGIN

and that you do not enable "Secure Password Authentication (SPA)" on the client unless you've done the necessary preparations.

Aki

OK, I was chasing log ghosts. What was actually going on was fail2ban was kicking on for users and banning them for 10 min.

I have no idea what is triggering it for so many different users from legit email addresses. Still investigating. But this appears to be a fail2ban problem, not a dovecot problem.

On Jan 22, 2024, at 10:41 AM, Steve Dondley via dovecot <dovecot@dovecot.org> wrote:

Based on your email I went back and took a closer took at the logs.

The client reported this happened at 11:58 of the 19th. I went back and took a closer look and around 11:56 I found these entries in the log.

81218 Jan 18 11:56:56 ip-172-30-0-131 dovecot: imap(t.olixxxx)<3739040></ Z84+joPNhRsOgYu>: Connection closed (IDLE running for 0.001 + waiting input for 1175.376 secs, 2 B in + 10 B out, state=wait-input) in=182 out=172366 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0 81219 Jan 18 11:56:56 ip-172-30-0-131 dovecot: imap (s.damxxxx)<3739037><iQY3+joPottsOgYu>: Connection closed (IDLE running for 0.001 + waiting input for 1174.763 secs, 2 B in + 10 B out, state=wait-input) in=182 out=799331 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0 81220 Jan 18 11:56:59 ip-172-30-0-131 postfix/smtpd[3740240]: warning: hostname 179.hosted-by.198xd.com does not resolve to address 45.129.14.179: Name or service not known 81221 Jan 18 11:56:59 ip-172-30-0-131 postfix/smtpd[3740240]: connect from unknown[45.129.14.179] 81222 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap (j.pomexxxxx)<3739095><k7z3/zoPqLdsOgYu>: Connection closed (IDLE running for 0.001 + waiting input for 1078.221 secs, 2 B in + 10 B out, state=wait-input) in=165 out=801497 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count= 0 body_bytes=0 81223 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap (a.cerxxxxx)<3739042><JCXQ+joPu5JsOgYu>: Connection closed (IDLE running for 0.001 + waiting input for 1169.527 secs, 2 B in + 10 B out, state=wait-input) in=182 out=303618 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0 81224 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap (h.foxxxxx)<3739034><kpEo+joP9g5sOgYu>: Connection closed (IDLE running for 0.001 + waiting input for 1180.675 secs, 2 B in + 10 B out, state=wait-input) in=194 out=1927 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 bo dy_bytes=0 81225 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap(dxxxxxx)<3739057><xljV/ DoPPnZsOgYu>: Connection closed (IDLE running for 0.001 + waiting input for 1135.454 secs, 2 B in + 10 B out, state=wait-input) in=182 out=458253 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 bod y_bytes=0

So these have real user names associated (have been obfuscated. I think these are more likely the source of the error some users have been seeing, not the errors I originally posted here to the mailing list.

On Jan 21, 2024, at 8:34 PM, Benny Pedersen <me@junc.eu> wrote:

Steve Dondley via dovecot skrev den 2024-01-22 02:18:
     I have a mail server using dovecot that has  been running
     without issue for quite a couple of years now. It serves
     email for about 30 individuals.
     But since Jan 14th, users have been reporting spurious
     errors in MS Outlook:
      324 Jan 21 00:38:17 ip-172-30-0-131 dovecot: pop3-login:
     Disconnected (no auth attempts in 0 secs): user=<>,
     rip=118.xxx.xxx.xxx, lip=172.30.0.131, TLS handshaking:
     read(size=596) failed: Connection reset by peer,
     session=<mu/JHm4Ptup2wSuN>

there is no user in the above line

     Some characteristics of the problem that may offer a clue:
     * happening with multiple users, not just the same one
     * happens from different IP addresses.

bots detected

     * happens about 3 to 5 times per day and the errors come in
     batches like above
     * MS Outlook error is:

why is it a microsoft problem now ?

     reported error (0x80042109): ‘Outlook cannot conect to your
     outgoing SMTP email server. If you continue to receive this
     message….blah blah blah

disable pop3 in dovecot, problem is then gone

     I googled the error code but didn’t find anything
     particularly helpful.

we all use minimal tls1.2, the bots still use ssl, with username
fails

     I’m running Debian bullseye, version 11.8.

irelevant info

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To unsubscribe send an email to dovecot-leave@dovecot.org

---

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OK, I was chasing log ghosts. What was actually going on was fail2ban was kicking on for users and banning them for 10 min. 

I have no idea what is triggering it for so many different users from legit email addresses. Still investigating. But this appears to be a fail2ban problem, not a dovecot problem. 

 On Jan 22, 2024, at 10:41 AM, Steve Dondley via dovecot
 <dovecot@dovecot.org> wrote:

 Based on your email I went back and took a closer took at the logs.

 The client reported this happened at 11:58 of the 19th. I went back
 and took a
 closer look and around 11:56 I found these entries in the log.

  81218 Jan 18 11:56:56 ip-172-30-0-131 dovecot: imap
 (t.olixxxx)<3739040></
 Z84+joPNhRsOgYu>: Connection closed (IDLE running for 0.001 + waiting
 input for
 1175.376 secs, 2 B in + 10 B out, state=wait-input) in=182 out=172366
 deleted=0
 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0      
  body_bytes=0
  81219 Jan 18 11:56:56 ip-172-30-0-131 dovecot: imap
 (s.damxxxx)<3739037><iQY3+joPottsOgYu>: Connection closed (IDLE
 running for
 0.001 + waiting input for 1174.763 secs, 2 B in + 10 B out,
 state=wait-input)
 in=182 out=799331 deleted=0 expunged=0 trashed=0 hdr_count=0
 hdr_bytes=0
 body_count=0        body_bytes=0
  81220 Jan 18 11:56:59 ip-172-30-0-131 postfix/smtpd[3740240]:
 warning:
 hostname 179.hosted-by.198xd.com does not resolve to address
 45.129.14.179:
 Name or service not known
  81221 Jan 18 11:56:59 ip-172-30-0-131 postfix/smtpd[3740240]:
 connect from
 unknown[45.129.14.179]
  81222 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap
 (j.pomexxxxx)<3739095><k7z3/zoPqLdsOgYu>: Connection closed (IDLE
 running for
 0.001 + waiting input for 1078.221 secs, 2 B in + 10 B out,
 state=wait-input)
 in=165 out=801497 deleted=0 expunged=0 trashed=0 hdr_count=0
 hdr_bytes=0
 body_count=       0 body_bytes=0
  81223 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap
 (a.cerxxxxx)<3739042><JCXQ+joPu5JsOgYu>: Connection closed (IDLE
 running for
 0.001 + waiting input for 1169.527 secs, 2 B in + 10 B out,
 state=wait-input)
 in=182 out=303618 deleted=0 expunged=0 trashed=0 hdr_count=0
 hdr_bytes=0
 body_count=0        body_bytes=0
  81224 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap
 (h.foxxxxx)<3739034><kpEo+joP9g5sOgYu>: Connection closed (IDLE
 running for
 0.001 + waiting input for 1180.675 secs, 2 B in + 10 B out,
 state=wait-input)
 in=194 out=1927 deleted=0 expunged=0 trashed=0 hdr_count=0
 hdr_bytes=0
 body_count=0 bo       dy_bytes=0
  81225 Jan 18 11:57:00 ip-172-30-0-131 dovecot: imap
 (dxxxxxx)<3739057><xljV/
 DoPPnZsOgYu>: Connection closed (IDLE running for 0.001 + waiting
 input for
 1135.454 secs, 2 B in + 10 B out, state=wait-input) in=182 out=458253
 deleted=0
 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 bod      
 y_bytes=0


 So these have real user names associated (have been obfuscated. I
 think these
 are more likely the source of the error some users have been seeing,
 not the
 errors I originally posted here to the mailing list. 



     On Jan 21, 2024, at 8:34 PM, Benny Pedersen <me@junc.eu> wrote:

     Steve Dondley via dovecot skrev den 2024-01-22 02:18:
          I have a mail server using dovecot that has  been running
          without issue for quite a couple of years now. It serves
          email for about 30 individuals.
          But since Jan 14th, users have been reporting spurious
          errors in MS Outlook:
           324 Jan 21 00:38:17 ip-172-30-0-131 dovecot: pop3-login:
          Disconnected (no auth attempts in 0 secs): user=<>,
          rip=118.xxx.xxx.xxx, lip=172.30.0.131, TLS handshaking:
          read(size=596) failed: Connection reset by peer,
          session=<mu/JHm4Ptup2wSuN>

     there is no user in the above line

          Some characteristics of the problem that may offer a clue:
          * happening with multiple users, not just the same one
          * happens from different IP addresses.

     bots detected

          * happens about 3 to 5 times per day and the errors come in
          batches like above
          * MS Outlook error is:

     why is it a microsoft problem now ?

          reported error (0x80042109): ‘Outlook cannot conect to your
          outgoing SMTP email server. If you continue to receive this
          message….blah blah blah

     disable pop3 in dovecot, problem is then gone

          I googled the error code but didn’t find anything
          particularly helpful.

     we all use minimal tls1.2, the bots still use ssl, with username
     fails

          I’m running Debian bullseye, version 11.8.

     irelevant info

     _______________________________________________
     dovecot mailing list -- dovecot@dovecot.org
     To unsubscribe send an email to dovecot-leave@dovecot.org

 _______________________________________________
 dovecot mailing list -- dovecot@dovecot.org
 To unsubscribe send an email to dovecot-leave@dovecot.org

Yeah I think I figured it out. It looks like someone set up their phone with bad password and when they got on the WiFi network it got everyone else on the network banned for 10 min. I’ve whitelisted the ip for now. I think the guy was traveling between different offices making it look like it wasn’t isolated to a single network.

On Jan 22, 2024, at 6:15 PM, Michael Grant <mgrant@grant.org> wrote:

On Mon, Jan 22, 2024 at 04:28:09PM -0500, Steve Dondley via dovecot wrote:

...

OK, I was chasing log ghosts. What was actually going on was fail2ban was kicking on for users and banning them for 10 min.

I have no idea what is triggering it for so many different users from legit email addresses. Still investigating. But this appears to be a fail2ban problem, not a dovecot problem.

Oh you have my sympathies. fail2ban-client banned ipaddr. Get the ip addr of your users and see if they're banned like th is. Then use fail2ban-client unban. I can't tell you how often this happens to me.

What happens is users have phones and laptops and they then add a tablet and want their email on it so they end up messing up their password on their tablet, or worse, resetting their password in order to get mail on their tablet and then it screws up the other devices and it's an absolute nightmare to continually debug. It happens to multiple users who are at the same address, as in, my parents because they're all behind the same address in the router. It happens to multiple people who use New Outlook which insists on sucking all the mail into Microsoft's servers and then one user bans a swatch of addrs of those servers and random things break everywhere. I ended up whitelisting all of microsoft's mail servers in my jail.local:

40.80.0.0/12 40.74.0.0/15 40.120.0.0/14 40.125.0.0/17 40.76.0.0/14 40.96.0.0/12 40.124.0.0/16 40.112.0.0/13

Hope this helps. I have been there so many times and it's a regular occurance in my tech life chasing these ghosts.

Michael Grant