Thunderbird cannot send emails today (after many years)

[#1]

Webmail works.

I see this sort of thing has cropped up in the past - so hopefully it is a spot of indigestion on the PlusNet/Force9 relay servers.

Bit of a pain though.

Looks like Thunderbird might hook up to both Gmail and Yahoo and bypass PlusNet/Greenby or whoever it is currently.

[#2]

Just a quick message to say that I ran into a problem sending mail through relay.force9.net today. I have been using no encryption or security settings on a direct line to Plusnet and all of a sudden, SMTP requests were failing with "451 4.3.2 Internal server error". I had to change the settings as follows:

Port from 25 to 587
Security to SSL / TLS via STARTTLS
Authentication to Log on using a POP3 username and password

I was not using Thunderbird, so the actual settings may be slightly different for you. That allowed me to send a test e-mail immediately.

I hope that helps (with thanks to other Community Denizens).

[#3]

Thanks - I tried this but to no effect.

It had occurred to me that this problem has arisen after Cloudflare updated, even though Cloudflare is normally off or "disconnected"

Anyone else have experience of Thunderbird and Cloudflare?

 I know that Cloudflare does block Thundrerbird, but not webmail. I normally leave Cloudflare off - I only started using it when Plusnet, BT etc all blocked Anna'sArchive on December 24th last year.

Of course the problem COULD be Greenby related. But the timing of it suggests otherwise to me.    

[#4]

Also having problems using Thunderbird, but it depends on the recipient. Mails get sent but never arrive, without bounce.

Using SMTP relay.plus.net, port 587, STARTTLS, no authentication

At the moment, nothing I send arrives at btinternet.com addresses.

Sending to gmail addresses it happens maybe 10% of times.

Others it works fine.

[#5]

Interesting you should mention Gmail

This is my attempted recipient + TBird response

"An error occurred while sending mail. The mail server responded:
Internal server error.
Please check the message recipient "[Removed]@googlemail.com" and try again"

If I copied and pasted everything to PlusNet webmail it would work

which kinda negates the benefits iof having Thunderbird in my view

Moderator's note by Mike (Mav): Personal information removed from a public forum (to an area that staff can see).

[#6]

It looks more like a blacklist problem. If that's the case, please can you speed up the migration to Greenby who probably have a clean slate... plusnet email is getting very unreliable.

[#7]

Folks, it is important to distinguish clearly between the email brands, especially for sending issues.  Force9 and Free-online are via the Greenby proxy server, which is independent of the the migration status of an email account.

[#8]

Ok, which thread here is the most appropriate for sending issues using relay.plus.net?

[#9]

No specific thread, but just be clear when posting "I have the same problem".

Until verified with precise details, in general problems only have similar appearances until correlation of details verifies that they are the same.

Similarly is the importance between "cannot send emails" and "emails sent have not arrived" - they are very different matters.  Being able to send, but they not arriving eliminates all of the potential connection issues which might give rise to the claim "cannot send emails" as per this thread, which actually talks of them not arriving - a rather different statement.

Server connection issues can be flushed out for each brand using the server connection diagnostic - see the link below.  Emails accepted but not delivered needs different analysis.

[#10 · Accepted solution]

Further to the above - Thunderbird has a Troubleshooting mode - which I entered

This then cause a demand for a password when sending emails.

Since entering the password everything seems to work.

So my guess is this. The system had been set up not to require authentication on sending emails.

This mucking about with Greenby seems to have changed that. Now a password is required.

That's my guess - until a Superuser comes yup with a better answer.  

[#11]

@ColdharbourDave 

Which email brand?

[#12]

Force9 - i've not had any "official notification" about transfer to postmaster@myaccount (which was always supposed to be the correct procedure.

I got the following message on my "normal" email address on 17th September 2025

Hello David, We are making some changes to your email, david@xxxxx.f9.co.uk. To ensure you can continue to receive a reliable and secure email service, we’ve taken the decision to transfer the running of our email to the provider Greenby who will manage the service going forward.

Why Greenby?

	Greenby are part of the Enix group who are one of the leading providers for email services and web hosting. You can find more information on Greenby and Enix at enixltd.com. Greenby are one of the most reliable email providers available and can provide you with the following features: • Retain your current email address and inbox content • A specialist team to assist you with your service and any queries • Easy to use platform We’ve arranged for the service to be free of charge for the first two years, Greenby will then confirm any future charges.

What do I need to do now?

	To continue to send and receive emails after the migration, you need to make a change to how you access your mailbox. You need to log in going forward with the username scriabin+david. Your password remains the same. For further guidance on this, please click here. This change needs to be made before 31st October 2025. If you already log in this way, you don’t need to take any further action. Greenby will then be in touch when the transfer is complete and will provide you with details on how to set up payment. No payment will be taken during the first 2 years or without your authorisation. Once you have been transferred, Greenby will become responsible for the personal data that is processed to provide your email service (including name, contact details, login details and mailbox data). You can view Greenby’s privacy notice by clicking here. To find out more on the migration, visit our FAQs page. View FAQ's page

How to opt out

	If you don’t use your email or don’t wish us to transfer your data to Greenby, you can opt out of the transfer by clicking here before 30th September 2025. If you do not opt out of the transfer by this date, your mailbox or service will still migrate to Greenby. Please be aware that if you choose to opt out, you will lose access to your email address, email data and all mail stored within the account. You can view Greenby’s privacy notice by clicking here. Thank you for being with Plusnet

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