Emails sent from GMail through Thunderbird bounced by Plusnet and xtra.co.nz

[#1]

I use Thunderbird to run all my email, including GMail, and I've noticed today that any GMail message of any kind sent by me through POP on Thunderbird (52.6.0) is being bounced by PlusNet as "552 Spam Message Rejected", whilst the same message composed and sent from the GMail website is not bounced. 

The same appears to be happening with mail sent to Xtra.co.nz (an email service of Spark in New Zealand), but their bounce is "554 5.7.1 Message rejected due to possible spam content".  Again sending the same message through GMail's website results in delivery.  Likewise perhaps with Centurytel.net "554 5.7.1 [P4] Message blocked due to spam content in the message".

Any ideas?

[#2]

Your message is being rejected by our outbound mail servers (relay.plus.net). This means that you're using Plusnet's servers to send your non-Plusnet hosted email.

Whilst this wouldn't normally present a problem, you might want to look into using Google's servers to relay your GMail messages instead.

If you can send the Gmail message to your own Gmail address via the Webmail interface and then provide me with a copy of the received email source (see below), then I should be able to work out what's going on.

Would suggest sending the message via Private Message rather than posting here.

[#3]

Sorry I didn't mean POP I meant SMTP.

I am sending a message from my GMail account, using smtp.gmail.com , from the email program Mozilla Thunderbird.  When I send any message this way at the moment, even just a few words of text, if the recipient is a Plusnet customer it is being bounced back as spam.

Here is the result:

Message not delivered There was a problem delivering your message to peter@?????????.plus.com. See the technical details below, or try resending in a few minutes.

The response was: 552 Spam Message Rejected

Reporting-MTA: dns; googlemail.com
Received-From-MTA: dns; p????????@gmail.com
Arrival-Date: Fri, 23 Feb 2018 03:30:19 -0800 (PST)
X-Original-Message-ID: <e3384b12-2487-4aac-1371-beaf3c84f8cd@gmail.com>

Final-Recipient: rfc822; peter@?????????.plus.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; mx.avasin.plus.net. (212.159.9.200, the server for the domain reynoldsbooks.plus.com.)
Diagnostic-Code: smtp; 552 Spam Message Rejected
Last-Attempt-Date: Fri, 23 Feb 2018 03:30:23 -0800 (PST)

About a dog.eml

Subject: About a dog

From: Peter Reynolds <p????????@gmail.com>

Date: 23/02/18 11:30

To:

peter@????????.plus.com

I have to go and see a man about a dog.

[#4]

By contrast, exactly the same subject and text sent from GMail's website goes through just fine.

[#5]

It looks like one or more of the smtp.gmail.com relays has been blacklisted by the Plusnet Cloudmark appliances as a source of spam. The MX at xtra.co.nz appears to take the same view.

Do any of the non delivery report messages you've received mentioned the sender IP address(es) involved?

[#6]

---

@PeterPiper wrote:

I am sending a message from my GMail account, using smtp.gmail.com , from the email program Mozilla Thunderbird.  When I send any message this way at the moment, even just a few words of text, if the recipient is a Plusnet customer it is being bounced back as spam.

---

The advice is the same as my previous post. Send one of the offending messages to your Gmail address (i.e. to yourself), and provide the original source of the received email. Examining this source will allow me to see where the problem lies.

Don't post it here, send it to me directly.

[#7]

Bob

Thank you.  I've done that now.

Kind regards

Peter