Problems sending PN email to Gmail addresses

[#1]

Re your new greylisting theory, what do you mean by a "retransmitted" email?

If you mean (in my case) retransitted by Plusnet to Google, then aren't everyone's emails retransmitted all the time?

Or am I missing the point?

[#2]

If you mean (in my case) retransitted by Plusnet to Google, then aren't everyone's emails retransmitted all the time?

They are, but when greylisting is being used. the receiving MTA initially temporarily deliberately rejects the email by sending a 'please try later' response. It then 'remembers' the source of the email. If the sender delays then retries within a certain period, then the email is subsequently accepted. Because Plusnet have a group of MTAs with different IP addresses, if gmail are looking for the source of the retransmitted email to be 'exactly' the same i.e from the same IP, then it MAY not match. Eventually the retried email MAY come from the same MTA and thus be accepted.

I used to have greylisting enabled on our office email system, but TBH it caused more problems than it avoided.

I may be barking up the wrong tree completely but the fact that the delay seems random could fit a badly implemented greylisting situation.

[#3]

Thanks. That's clear and very helpful.

Two questions (and forgive the ignorance if these are dumb ones);

1) Would the 'please try later' response not show up in the headers?

2) Is Plusnet the only email provider to use multiple MTAs with different IP addresses?

If NO, why are other providers (as far as we know) not having similar issues with Gmail?

If YES, why is Plusnet out of line with other providers in this respect?

[#4]

I understand the idea that greylisting can deter spammers because spammers don't usually re-try,

but isn't the theory of greylisting that when a re-try is successful you get whitelisted and the problem goes away?

[#5]

1) Would the 'please try later' response not show up in the headers?

No, its purely an SMTP code transmitted between the receiving & sending MTAs

2) Is Plusnet the only email provider to use multiple MTAs with different IP addresses?

TBH I don't know, but I wouldnt have thought so.

From my tests, my domain hosting is using IPv6 to send to gmail, whereas the PN servers will be using IPv4 addresses, so any subnet matching will be completely different.

but isn't the theory of greylisting that when a re-try is successful you get whitelisted and the problem goes away?

yes, it is , but you are only whitelisted for some defined period.

[#6]

Hi Mister W,

Now we're past the weekend and back to normal staffing levels, do we know if Plusnet's technical team are actively investigating the Gmail problem , checking mail server logs etc? 

I know there's a limit to what you can do yourself, but I think customers deserve fairly frequent status reports from the company when things like this go wrong, even if initially that's just to acknowledge that the fault exists!

[#7]

I havent heard anything yet. I'll give them a prod...

[#8]

@PeterB1  its actively under investigation on the same Incident reference as the problem with sending to Microsoft.

I've asked for something to be added to the Service Information board https://community.plus.net/t5/Service-Information/bd-p/ServiceStatus

[#9]

Thanks, Mister W.

But nothing visible on the Service Information Board as yet.

The link in your post connects to an item about the Microsoft problem dated September 2024 and there is no mention of Gmail.

[#10]

The link in your post connects to an item about the Microsoft problem dated September 2024 and there is no mention of Gmail.

The Sept 2024 is the date the poster registered on the forum. The post relates to the recent MS problem.

I know its not ideal, but getting things on the Service board does seem to take some time... 

[#11]

It's Tuesday 01 Jul 2025 at 09:23 and emails I send from my xxxxxx.plus.com address are still not arriving at GMail. This started for me with extreme delays over the weekend (4 hours), then emails silently disappearing - as for others here.

I just tried using my Plusnet-hosted domain name address, however and that arrived at GMail immediately ( < 30 secs). It has an SPF record of

;; ANSWER SECTION:
xxxxxxx.co.uk. 14317 IN TXT "v=spf1 a mx include:_spf-internal.plus.net include:_spf-internal2.plus.net ~all"

and the headers show spf=pass

Received-SPF: pass (google.com: domain of yyy@xxx.co.uk designates 212.159.14.17 as permitted sender) client-ip=212.159.14.17;

[#12]

Hi disfroot,

Like you, I'm also finding that emails send to Gmail accounts from my xxxx@yyyy..plus.com address are either arriving very late or disappearing.

However, as with the emails sent from your Plusnet-hosted domain name address, it's not SPF or any of Gmail's other authentication requirements that are causing the problem. Examining the headers of my emails that are eventually delivered shows they pass all of these Gmail tests and are processed more or less instananeously by Gmail. once they're received by the Gmail server. 

The delays are happening before the emails leave Plusnet.

Why is anybody's guess!

[#13]

"Why" is a very easy "guess" - Gmail are backing off acceptance of the initial and subsequent attempts to deliver the email.

This is technique used (abused) for various reasons.  We saw the exact same behaviour from Gmail a couple of years ago - the random disinclination by Gmail to receive mail to FREE Gmail accounts.  PAID for Gmail accounts were not affected, sending to @googlemail.com instead of @gmail.com (they are equivalent) were also not affected.

That was mitigated by the introduction of DKIM and DMARC to *.plus.com.  Those accounts now also have SPF - there is ZERO justification for the current Gmail activity.

[#14]

If that were the correct explanation, why also apparently the same problem with Microsoft addresses in the same time frame? You're effectively also saying that the Google mail servers are not RFC-compliant by not sending the appropriate bounce or delivery-reattempted message back to the originator.  Do we know that to be true?

[#15]

A couple of questions for Townman.

1) I had heard the Microsoft issue was technically different from the Gmail one.

Can you confirm?

2) If your analysis of the Gmail problem is correct (i.e. Gmail playing silly b......rs) - what are the prospects for mitigating/resolving? 

I understand from MisterW it is offiicially being investigated, but there is no confirmation of this in the Service Information section of this forum.

It's knowing nothing that makes life so difficult !!!