Delivery failed to Gmail address via an alias

[jbuchanangb]

I sent an email to an Ionos managed alias address which forwards mail to a Gmail address. I usually send to that person using their Gmail address directly but this time I was using "Reply-All" to an email where the originator had used the other person's email alias.
This is the non delivery report (I have replaced the person's name with the word "user":

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.

The following address failed:

    user.shorelinechurch@gmail.com:
        SMTP error from remote server for TEXT command, host: gmail-smtp-in.l.google.com (173.194.76.27) reason: 550-5.7.26 Unauthenticated email from talktalk.net is not accepted due to
550-5.7.26 domain's DMARC policy. Please contact the administrator of
550-5.7.26 talktalk.net domain if this was a legitimate mail. To learn abo ut
550-5.7.26 the DMARC initiative, go to
550 5.7.26  https://support.google.com/mail/?p=DmarcRejection ffacd0b85a97
d-385e907a6easi2682030f8f.214 - gsmtp


--- The header of the original message is following. ---

UI-Loop: V01:97MgnqHwelU=:OPu+Z2f8i6Rh+04FHq13KveIDiOErnzqMSE6MNquBEs=
Received: from mx004.tt.xion.oxcs.net ([153.92.124.205]) by mx.kundenserver.de
 (mxeue103 [217.72.192.67]) with ESMTPS (Nemesis) id 1N1eBy-1tg9Bt44Wu-015KdU  for <user@shorelinechurch.org.uk>; Mon, 02 Dec 2024 16:14:54 +0100
Received: from proxy-20.proxy.shared.ns.xion.oxcs.net (proxy-20.proxy.shared.ns.xion.oxcs.net [2.102.196.45])
	by mx-out.tt.xion.oxcs.net (Postfix) with ESMTPA id 333E2A40301;
	Mon,  2 Dec 2024 15:14:47 +0000 (UTC)

I have resent my email using the person's Gmail address directly, without a failure message. Is there something to investigate here?

[jbuchanangb]

To avoid putting actual email addresses in the forum, I have sent you a PM.

[Ady-TalkTalk]

Hi Jbuchanangb, OX are asking for your sending address and the direct receiving address. Are you sending direct to an MS hosted address? Or are is the mail forwarded? 

Ady

[jbuchanangb]

This error has occurred again. Same destination address, also as one of a list of addressees, as before. Sending to this addressee as the sole recipient does not cause the error. Maybe it is worth a little more investigation.

[jbuchanangb]

I'm not sure if I understand this. If I send from any email address (Talktalk, Tiscali, or Hotmail) to an address managed by IONOS where the destination is my TalkTalk email address I can see from the message headers that it goes via servers at kundenserver.de where it gets translated into my TalkTalk address and comes back to me.
I can see that I have successfully sent from my Tiscali and from my TalkTalk address to various users @shorelinechurch.org.uk. These go via IONOS and the kundenserver.de servers. Most of those emails get through. In this case used "Reply-All" to an email which included an alias. In fact 3 of the addresses were @shorelinechurch.org.uk. Only one of them was bounced by Gmail.
If I understand the headers correctly the message was received by mx.kundenserver.de from mx004.tt.xion.oxcs.net.
So far so good. Its next move would have been for kundenserver.de to send it off in the direction of Gmail.
But for some reason kundenserver.de has rejected it. kundenserver is saying that it couldn't send it on to gmail-smtp-in.l.google.com, because Gmail wouldn't accept it.
Anyway. I have just sent a test massage to the actual email address which failed, and it has been successful. The recipient has replied to confirm it. So it's not worth spending any more time on it. Just some strange glitch.

[Ady-TalkTalk]

Since the mail platform migration to OX mail forwarding through TalkTalk smtp servers has not been possible. 

Ady

[jbuchanangb]

I consider this to be a fault, rather a strange one, but a fault nevertheless, so please raise a fault ticket. Hopefully we can follow up, and if necessary I can attempt to replicate it at some time in the process. Plenty of people send to me using an Ionos managed alias which forwards to my talktalk.net email address. I should be able to send to such an alias which forwards to a Gmail address.

[Ady-TalkTalk]

Hi jbuchanangb, if you'd like I can raise a fault ticket for you. I have no access to quicker processes now so that would be the only option.

Ady