Mail bounced due to DMARC error

[scletts1]

I can't send email from lineone to an address that is then redirected to gmail.

Here's the bounce message:

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

xxxx@gmail.com
(ultimately generated from yyyyy@zzzzz.co.uk)
host gmail-smtp-in.l.google.com [173.194.219.26]
SMTP error from remote mail server after end of data:
550-5.7.26 Unauthenticated email from lineone.net is not accepted due to
550-5.7.26 domain's DMARC policy. Please contact the administrator of
550-5.7.26 lineone.net domain if this was a legitimate mail. To learn about the
550-5.7.26 DMARC initiative, go to
550 5.7.26 https://support.google.com/mail/?p=DmarcRejection 3f1490d57ef6-e39f6c458a4si7019159276.86 - gsmtp

Reporting-MTA: dns; raz.smoothhost.com

Action: failed
Final-Recipient: rfc822;yyyyy@zzzzz.co.uk
Status: 5.0.0
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.26 Unauthenticated email from lineone.net is not accepted due to
550-5.7.26 domain's DMARC policy. Please contact the administrator of
550-5.7.26 lineone.net domain if this was a legitimate mail. To learn about the
550-5.7.26 DMARC initiative, go to
550 5.7.26 https://support.google.com/mail/?p=DmarcRejection 3f1490d57ef6-e39f6c458a4si7019159276.86 - gsmtp

[Ady-TalkTalk]

Send me a personal message with the affected email addresses please. 

Ady

[scletts1]

Hi Ady,

Thanks for your quick reply but I don't believe it deals with the issue.

You say "TalkTalk outgoing mail servers don't allow unauthenticated mail sending" but that isn't the problem, I can send mail OK, I use smtp.talktalk.net together with my lineone address and password.

The problem only happens when I send to one particular address. The user redirects his emails to gmail, which bounces messages from me. It does not bounce redirected email from other people.

The error message says the problem is at lineone. As I showed you in my first message it says, "Unauthenticated email from lineone.net is not accepted"

My mail is sent from an authenticated TalkTalk email domain, it is redirected by an intermediate server and is then bounced by gmail.

I don't understand what's happening, can you investigate some more?
Simon

[Ady-TalkTalk]

Hi scletts1, TalkTalk outgoing mail servers don't allow unauthenticated mail sending. The mail must be sent from an authenticated TalkTalk email domain. 

Ady