Mail delivery failures when sending from onetel account through relay.plus.net

[#1]

Hi one of my main accounts is  dxxxxxxxxxxxx@onetel.com.  I have used this for years via plusnet without problems, including the use of relay.pus.net for outgoing messages.  Just recently, if forwarding a message I have received a mail delivery failed message saying    ** The remote server ?? responded with: ** xxx@yyyy.com ??:?

Usually it affects just one or two addresses in a circulation, usually a TalkTalk address.   But I have just had 17 out of 25 of a circulation in a 'reply all' message rejected.  Most are gmail and talktalk addresses but yahoo, AOL and icloud appear too.  Messages in the circulation to btinternet, plusnet, outlook and hotmail addresses have not been rejected.

I have resent the message using one of my plusnet.com addresses and have had no rejections.  Any ideas what might be going on?

David

[#2]

I have looked more closely at the reject message details.txt files.  DMARC issues are often mentioned while one gmail response said "Unauthorised email from onetel.com is not accepted."

No idea how to follow these up.

[#3]

It is very probably due to SPF , read about it here https://en.m.wikipedia.org/wiki/Sender_Policy_Framework

In a nutshell , your onetell domain does not have relay.plus.net as an authorised sender. You either have to send from a onetell server or add relay.plus.net to an authorised list by adding an spf record ( probably not possible )

[#4]

Thanks Mr W.  That sounds like the problem.   Although why this is occurring just now... and is getting progressively worse (direct, single mailings are also now being rejected) is a bit of a puzzle.  It sounds like TalkTalk have tightened their anti-spam procedures without appreciating the full consequences.

Plusnet have previously requested me to use relay.plus.com for ALL SMTP messages irrespective of domain.  Can I revert to a onetel specific server to get round this problem?

[#5 · Accepted solution]

@oneteldave Many mail systems are now starting to tighten their anti-spam and SPF together with DKIM and DMARC are being used more widely.

Reverting to using the onetel SMTP server for those email accounts is the best thing.

[#6]

Thanks Mr W.  That's sorted it.

[#7]

Well I thought it had!    It seems the rot is spreading.  I have just had 5 emails rejected (4 talktalk and one tiscali) when 'replying all' to a message originally sent to one of my plusnet accounts and replied to from the same account.  The original circulation was about 26 recipients long.  gmails were not affected and there were no other talktalk related addresses in the list. 

Am I alone in suffering this issue?

Regards

David 

[#8]

Somewhat bizarre I know, but I have just 'forwarded' the original 'sent' message to the recipient addresses that got rejected (from the same plusnet account) and received no rejections!   What IS going on?? 

The original rejection message details show "550 5.1.0 WLQZlJofUSFlQ Sender Domain Invalid (TT403)".

[#9]

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@oneteldave wrote:

The original rejection message details show "550 5.1.0 WLQZlJofUSFlQ Sender Domain Invalid (TT403)".

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From a cursory Google search that sounds like a Talk Talk error that is spewed out in response to a variety of issues relating to outages within Talk Talk's mail platform, so it'd be one to raise with them if it persists.