Forwarded email bouncing

[#1]

I have a domain with Plusnet with several mail forwarders configured on it. Those mail forwarders channel incoming mail to Gmail addresses, since I host all my mail on Gmail.

This has worked perfectly for several years, but I've now got a problem where some -- but not all -- incoming mail isn't being forwarded, but is returning the following error to the sender:

A message that you sent to the following recipient could not be delivered due to a permanent error. ** The remote server ?? responded with: ** [validaddress]@gmail.com ??:?? This message was created automatically by mail delivery software on the server .

Note that the ** and ?? in this text are as included in the bounce message, and not to redact data for posting here.

From another domain, not hosted with Plusnet, messages continue to forward correctly to the same receiving Gmail accounts, so I'm fairly convinced the problem is with Plusnet and not with Gmail.

Any ideas?

[#2]

I had exactly this this morning.

It appears to be that Plusnet's outgoing server is listed on at least the abusix blocklist. Doesn't seem to be on any of the Spamhaus ones. This needs someone at Plusnet to contact abusix and sort it out.

My bounce also had this information; the same email was received by the half a dozen others cc:d on it. I use mail.plus.com as my relay.

Final-recipient: rfc822; <redacted>
Diagnostic-Code: smtp; 554 5.7.1 Service unavailable; Client host [212.159.14.20] blocked using urbl.hostedemail.com; https://www.abusix.ai/search?q=212.159.14.20

[#3]

@Gandalf @bobpullen Could you bring this thread to the attention of the relevant team internally, please?

Also this one, which is the same issue.

[#4]

Hi @garywood84, sorry for us taking so long to respond. I'll get this flagged up to Anoush/Bob for you to make sure it's looked at on Monday.

[#5]

Thanks, @adamwalker. 

I raised a ticket on this, and Josh Berriman has been reviewing it with me. But if there's anything you can do to expedite resolution, I'd appreciate it! 

Have a good weekend mate.

[#6]

I can see Josh has raised a NetOps task and he'll get back to you shortly about that.

In the meantime, if you turn off the auto-forwarder do you receive mail okay? If you do, then what happens if you manually forward an email that's normally rejected to your Gmail address? Does that bounce?