Cannot send any Plusnet emails

[#1]

I hope it works for you. I have been waiting 9 days now without being able to send or reply to emails with the same error message as you.

[#2]

Oh no, hope you get sorted soon. I've just replied with the details and will keep my fingers crossed.

[#3]

Same message - cannot send mail from iMac (Tahoe 26.2), nor can I send from iOS devices (also 26.2).  Ran diagnostics as per another thread, no issues arising as Imap works and smtp shows authorisation successful and am receiving emails as well.  Weird thing is I can send from the Greenby/Plusnet webmail!  Been out of action for two days now.