They may be the cause of the "still trying" messages - but in this case the messages were delivered OK.

Help would be greatly appreciated regarding the following three questions about  "421 Service Temporarily Unavailable"

Please explain what is occurring when "421 Service Temporarily Unavailable" is logged.

Does the sender receive a notification of the temporary failure?

Do the log entries below indicate the messages were actually sent (wondering what the "processing complete" entries actually mean)?  Neither of these IP address appear later in the log yet the mail queue is empty.

T 20151026 185534 562e0aa9 Established ESMTP connection to 216.82.251.230
T 20151026 185534 562e0aaa Established ESMTP connection to 85.158.139.103
W 20151026 185534 562e0aa9 421 Service Temporarily Unavailable
E 20151026 185534 562e0aa9 TCP/IP error.
T 20151026 185534 562e0aa9 Job MO0000F1 processing complete.
W 20151026 185534 562e0aaa 421 Service Temporarily Unavailable
E 20151026 185534 562e0aaa TCP/IP error.
T 20151026 185534 562e0aaa Job MO0000EE processing complete.

TIA,

Brian

[quote user="Brian Fluet"]

Help would be greatly appreciated regarding the following three questions about  "421 Service Temporarily Unavailable"

Please explain what is occurring when "421 Service Temporarily Unavailable" is logged.

Does the sender receive a notification of the temporary failure?

Do the log entries below indicate the messages were actually sent (wondering what the "processing complete" entries actually mean)?  Neither of these IP address appear later in the log yet the mail queue is empty.

T 20151026 185534 562e0aa9 Established ESMTP connection to 216.82.251.230
T 20151026 185534 562e0aaa Established ESMTP connection to 85.158.139.103
W 20151026 185534 562e0aa9 421 Service Temporarily Unavailable
E 20151026 185534 562e0aa9 TCP/IP error.
T 20151026 185534 562e0aa9 Job MO0000F1 processing complete.
W 20151026 185534 562e0aaa 421 Service Temporarily Unavailable
E 20151026 185534 562e0aaa TCP/IP error.
T 20151026 185534 562e0aaa Job MO0000EE processing complete.

TIA,

Brian

[/quote]

More information would be useful!

I'm guessing these are outgoing messages and the log is from Mercury C or E - is that correct?

Any 4xx message from a server is a temporary failure of some kind and the attempted delivery should be retried. It doesn't usually result in a non-delivery notification.

In this case it appears that the messages were delivered sucessfully with no noticeable delay.  A session log might help to give more information, but I usually associate 421 messages with greylisting or throttling of some sort.

More info...

I had a user ask me about two delivery notifications that said "still trying" but she deleted them before I had a chance to look at them.  I went to the MercuryE log to see what I could see and the entries I posted were around the time she said she had sent the original messages.  These were the only two "421 Service Temporarily Unavailable" entries in the log (about two months worth) so this appears to be a fluke but I was hoping to understand causes.

I assume from your response Paul that the "processing complete" entries mean the messages where delivered.  The fact that those entries occurred without delay is why I wondered whether these messages where indeed the ones that triggered the "still trying" notifications received by the user.