421 Downstream server error

[BobMc98]

MailEnable has been humming along for me for months with no issues. Then yesterday I started receiving bounceback messages with this error, which I haven't seen before.

From what I can gather, it means there is some low-level communications issue with the destination server for the recipient's domain. But I have been sending to this domain without issue for months. What would have changed?

There have been no changes to MailEnable or the OS, as far as I know. They recipient doesn't seem to have changed anything either.

Any suggestions regarding what to check? The log looks like this:

Fork/Split: Message ID [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] requeued/split into 1 messages for delivery to target domains.
Queued: Message ID [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] queued for delivery to the domain ["redacted".com] at the SMTP Outbound Queue with a new Message ID of [06BB632DD4A94BFDBE15D6F60299E6EC.MAI]

Status: SMTP Outbound Delivery details for Message ID [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] to domain ["redacted".com] follow below:
02/01/19 13:50:01 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2044 123.456.789.012 CONN 421 Downstream server error 0 29 me@"redacted".com RE: Status / Questions
02/01/19 13:50:01 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2044 123.456.789.012 QUIT QUIT - 6 0 me@"redacted".com RE: Status / Questions
02/01/19 13:51:04 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2044 123.456.789.345 CONN 421 Downstream server error 0 29 me@"redacted".com RE: Status / Questions
02/01/19 13:51:04 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2044 123.456.789.345 QUIT QUIT - 6 0 me@"redacted".com RE: Status / Questions
02/01/19 14:50:00 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2000 123.456.789.678 CONN 421 Downstream server error 0 29 me@"redacted".com RE: Status / Questions
02/01/19 14:50:00 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2000 123.456.789.678 QUIT QUIT - 6 0 me@"redacted".com RE: Status / Questions
02/01/19 14:51:03 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2000 123.456.789.901 CONN 421 Downstream server error 0 29 me@"redacted".com RE: Status / Questions
02/01/19 14:51:03 SMTP-OU 06BB632DD4A94BFDBE15D6F60299E6EC.MAI 2000 123.456.789.901 QUIT QUIT - 6 0 me@"redacted".com RE: Status / Questions


Debug delivery information for Message ID [06BB632DD4A94BFDBE15D6F60299E6EC.MAI]
02/01/19 13:48:57 ME-I0018: [B5BEE68ACA0E45B4A7826480A2B8F34F.MAI] Outbound message from ([SMTP:me@"redacted".com]) requeued as [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] to the target domain ["redacted".com]
02/01/19 13:48:58 ME-I0026: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Sending message
02/01/19 13:48:58 ME-IXXXX: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] DNS resolved to the following record: IP Address=123.456.789.012, Family=2, Type=1, Protocol=6
02/01/19 13:50:01 ME-I0009: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Remote server has closed connection after 0 milliseconds. Server Response: (-)
02/01/19 13:50:01 ME-I1350: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Attempting to connect to MX 2 of 2 (us-smtp-inbound-1.mimecast.com).
02/01/19 13:50:01 ME-IXXXX: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] DNS resolved to the following record: IP Address=123.456.789.345, Family=2, Type=1, Protocol=6
02/01/19 13:51:04 ME-I0009: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Remote server has closed connection after 0 milliseconds. Server Response: (-)
02/01/19 13:51:04 ME-E0059: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Message Delivery Failure. Attempt (2): Domain ("redacted".com) returned temporary error for email. Message has been requeued.
02/01/19 14:48:57 ME-I0026: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Sending message
02/01/19 14:48:57 ME-IXXXX: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] DNS resolved to the following record: IP Address=123.456.789.678, Family=2, Type=1, Protocol=6
02/01/19 14:50:00 ME-I0009: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Remote server has closed connection after 0 milliseconds. Server Response: (-)
02/01/19 14:50:00 ME-I1350: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Attempting to connect to MX 2 of 2 (us-smtp-inbound-1.mimecast.com).
02/01/19 14:50:00 ME-IXXXX: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] DNS resolved to the following record: IP Address=123.456.789.901, Family=2, Type=1, Protocol=6
02/01/19 14:51:03 ME-I0009: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Remote server has closed connection after 0 milliseconds. Server Response: (-)
02/01/19 14:51:03 ME-E0059: [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] Message Delivery Failure. Attempt (5): Domain ("redacted".com) returned temporary error for email. Message has been requeued.
02/01/19 14:51:03 [06BB632DD4A94BFDBE15D6F60299E6EC.MAI] caused a Delay Message to be generated with a Message ID of [E0591C4FA6D9494DAA90F4899EC36487.MAI]. The recipient of the delay is: me@"redacted".com


Thanks

[MailEnable-Ian]

Hi,

The domain is the mail address does not look to be formatted correctly. I.e: "redacted".com. How was the message generated? Do you have associated SMTP activity log snippet?