Why are messages queued and not sent with sendmail

sendmail

I am having trouble with one of my sendmail servers. Users are informing me about that registration emails do not arrive. The logfile claims that the message has been queued, but the queue is empty:

sudo cat /var/log/mail.log | grep email

(with obfuscated e-mail and server adresses in this example):

Jan 6 23:33:57 fx1 sendmail[9292]: u06MXvuk009292: to=email,
ctladdr=sender-email (1001/100), delay=00:00:00, xdelay=00:00:00,
mailer=relay, pri=38128, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0,
stat=Sent (u06MXv7o009293 Message accepted for delivery)

Jan 6 23:34:00 fx1 sm-mta[9295]: u06MXv7o009293: to=,
delay=00:00:03, xdelay=00:00:03, mailer=esmtp, pri=128308,
relay=mx3.hotmail.com. [65.55.37.120], dsn=2.0.0, stat=Sent (
<70001a6bb8ff80254895632a2c4367fb@myhost> Queued mail for delivery)

$ mailq
> MSP Queue status...
/var/spool/mqueue-client is empty
        Total requests: 0
MTA Queue status...
        /var/spool/mqueue (1 request)
-----Q-ID----- --Size-- -----Q-Time----- ------------Sender/Recipient-----------
u04ALref018750*     184 Mon Jan  4 11:21 <services@globosapiens.net>
                 (Deferred: Connection timed out with mail.vtmail.com.)
                     <nicolaitan@vtmail.com>
        Total requests: 1

The mail.err logfile is empty.

How could I track down the problem? This is happening quite frequently.

Best Answer

The log entry 

stat=Sent ( <remote-id> Queued mail for delivery)

indicates that the remote server accepted the message. From the perspective of your SMTP server is has been delivered. It is now in the next hop towards the recipients INBOX.

What happens from there is no longer your mailserver's responsibility and neither something you can easily debug from your end, if at all. But typically the message will move through SPAM and anti-virus filters etc. before ending up either in the recipient's INBOX, Spam folder or possibly silently discarded.

Ask the recipient to check their spam folder and if found there have them forward the message headers to you is one approach. Please also read the canonical Q&A's on preventing email getting marked as spam and Fighting spam, what can I do?

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