CentOS 5.8 | Sendmail 8.14.4
I used to think that if SendMail experienced a temporary (400-class) error during delivery, it would place the message in a deferred queue (e.g. /var/spool/mqueue) and retry an hour later. For the most part, that appears to be the case. But every now and then, I'll notice log entries like this (email/domains renamed to protect the innocent :-) ) :
Dec 5 01:43:03 foobox-out sendmail : qBE3l7js123022: to=<firstname.lastname@example.org>, delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=124588, relay=exbox.foo.com. [10.10.10.10], dsn=4.0.0, stat=Deferred: 421 4.3.2 The maximum number of concurrent connections has exceeded a limit, closing transmission channel Dec 5 01:53:34 foobox-out sendmail : qBE3l7js123022: to=<email@example.com>, delay=00:10:31, xdelay=00:00:00, mailer=relay, pri=214588, relay=exbox.foo.com., dsn=4.0.0, stat=Deferred: 452 4.3.1 Insufficient system resources Dec 5 02:53:35 foobox-out sendmail : qBE3l7js123022: to=<firstname.lastname@example.org>, delay=01:10:32, xdelay=00:00:01, mailer=relay, pri=304588, relay=exbox.foo.com. [10.10.10.10], dsn=2.0.0, stat=Sent (<SLDFKJSDLFKJSDLFKJLKDSJLKFJDSLFKJSDLKFJSD@BOX.senderdomain.com> Queued mail for delivery)
Why did Sendmail try again just 10 minutes after the first attempt and then wait another hour before trying again?
If this is expected behavior, what scenarios will cause this faster requeue interval to occur?