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On the morning of Friday 20th November there were no emails from my FreeBSD server, opal. These are generated daily by the periodic system under FreebSD, one email containing a system overview and one a security report for the previous 24 hours.
opal was up, so what was the cause of the non-appearance of the emails?
The clue was in /var/log/maillog:
Nov 20 03:17:42 opal sm-msp-queue[83606]: 0AK34MKC083509: to=root, ctladdr=root\ (0/0), delay=00:13:20, xdelay=00:00:10, mailer=relay, pri=120837, relay=[127.0\ .0.1] [127.0.0.1], dsn=4.0.0, reply=451 4.4.3 Temporary lookup failure of 127.0\ .0.1 at bl.spamcop.net, stat=Deferred: 451 4.4.3 Temporary lookup failure of 12\ 7.0.0.1 at bl.spamcop.net Nov 20 03:17:42 opal sm-msp-queue[83606]: 0AK34dM3083585: to=root, ctladdr=root\ (0/0), delay=00:13:03, xdelay=00:00:00, mailer=relay, pri=123842, relay=[127.0\ .0.1], dsn=4.0.0, reply=451 4.4.3 Temporary lookup failure of 127.0.0.1 at bl.s\ pamcop.net, stat=Deferred: 451 4.4.3 Temporary lookup failure of 127.0.0.1 at b\ l.spamcop.net
I run my own DNS, forwarding queries to the Cloudflare DNS servers (1.1.1.1 and 1.0.0.1). Hmm, what did nslookup tell me?
> bl.spamcop.net Server: 127.0.0.1 Address: 127.0.0.1#53 Non-authoritative answer: Name: bl.spamcop.net Address: 184.94.240.110 ** server can't find bl.spamcop.net: SERVFAIL
Bizarre that it returns the address, and then returns a SERVFAIL. I tried with Google DNS:
> server 8.8.8.8 Default server: 8.8.8.8 Address: 8.8.8.8#53 > bl.spamcop.net Server: 8.8.8.8 Address: 8.8.8.8#53 Non-authoritative answer: Name: bl.spamcop.net Address: 184.94.240.110
This failure was affecting both incoming and outgoing mail:
# mailq -Ac
/var/spool/clientmqueue (4 requests)
-----Q-ID----- --Size-- -----Q-Time----- ------------Sender/Recipient-----------
0AK7HWmR084402 2501 Fri Nov 20 07:17 MAILER-DAEMON
(Deferred: 451 4.4.3 Temporary lookup failure of 127.0.0.1 at)
root
0AK7HWmS084402 5506 Fri Nov 20 07:17 MAILER-DAEMON
(Deferred: 451 4.4.3 Temporary lookup failure of 127.0.0.1 at)
root
0AK34MKC083509 787 Fri Nov 20 03:04 root
(Deferred: 451 4.4.3 Temporary lookup failure of 127.0.0.1 at)
root
0AK34dM3083585 3801 Fri Nov 20 03:04 root
(Deferred: 451 4.4.3 Temporary lookup failure of 127.0.0.1 at)
root
Total requests: 4
I switched to OpenDNS servers as the forward target in the local DNS and mails started flowing again.
While reading the sendmail log, I found an unrelated
issue with dovecot:
Nov 20 10:14:37 opal dovecot[32592]: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=192.168.0.253, lip=192.168.0.4, TLS handshaking: SSL_accept() failed: error:14094416:SSL routines:ssl3_read_bytes:sslv3 alert certificate unknown: SSL alert number 46, session=<+iujHIe0YJzAqAD9> Nov 20 10:14:37 opal dovecot[32592]: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=192.168.0.253, lip=192.168.0.4, TLS handshaking: SSL_accept() failed: error:14094416:SSL routines:ssl3_read_bytes:sslv3 alert certificate unknown: SSL alert number 46, session=<TASlHIe0YpzAqAD9>
These errors are caused by GMail access from an Android phone. I remember a similar issue from a few months ago, which was cured by deleting the email account and re-creating it. So that's I did this time, except that the setup process told me the outgoing mail server did not offer STARTTLS. That's not right.
However, GMail was right...
[mark@opal:~]$ telnet localhost 25 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. 220 opal.hydrus.org.uk ESMTP Sendmail 8.16.1/8.16.1; Fri, 20 Nov 2020 10:41:41 GMT EHLO localhost 250-opal.hydrus.org.uk Hello localhost [127.0.0.1], pleased to meet you 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-8BITMIME 250-SIZE 250-DSN 250-ETRN 250-AUTH DIGEST-MD5 CRAM-MD5 250-DELIVERBY 250 HELP QUIT 221 2.0.0 opal.hydrus.org.uk closing connection Connection closed by foreign host.
No STARTTLS capability was being shown. I restarted the sendmail service many times by now, so that I actually managed to spot the error:
Nov 20 12:04:20 opal sm-mta[88853]: STARTTLS=server, error: SSL_CTX_check_private_key failed (PATHNAME ELIDED): 0
Sendmail was showing STARTTLS on crimson, the backup
server, so I compared configurations. I found a key difference in
the sendmail configuration file
(<machine_name>.mc):
define(`confSERVER_CERT', `CERT_DIR/cert.pem')dnl
define(`confSERVER_CERT', `CERT_DIR/chain.pem')dnl
Yet another shoot footing incident. I must have changed this sometime in the past for reasons I can no longer remember and hadn't noticed the effect. Shows how often I send mail out from a remote client using hydrus.org.uk.
Now, the fullchain.pem file is used to supply the SERVER_CERT and all is good.
At present, Cloudflare is resolving bl.spamcop.net
without error, but there does seem to be a small delay after the
address is returned in nslookup.
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