try port 587 for outgoing. if that doesn't work, try465 and SSL/TLS

Thanks, David. Unfortunately, neither of those worked, got the same error message.

The certificate error seems important. I suggest contacting the email provider.

Okay, shall try that, see what they say.

I tested the server here https://www.immuniweb.com/ssl/mail.optusnet.com.au/IdCIcYMJ/

While there is an unnecessary root certificate issued, that should not be a problem. So do you have an antivirus on your apple product? Perhaps one that scans encrypted connections and substitutes legitimate certificates for its own self signed ones.

Or a VPN that might lead Optus to think you are connected to the internet using a service other than theirs?

Thanks, Matt. No, I don't have antivirus and no VPN. I contacted Optus again today and they have set up a case to investigate the problem. Fingers crossed!

I don't think the problem is with Thunderbird. I have exactly the same problem with the email client on my phone, which is not Thunderbird. I've tried all the settings recommended by Optus (and even others), I have turned off antivirus and VPN, and nothing. The same result on both my laptop and phone. Seems a bit coincidental for me to have two different clients on two different devices having the same problem.

I agree with you, grahaman@optusnet.com.au. I'm pretty sure it's something at their end. Optus webmail went wonky around the same time/just before I started having the sending email problem with Thunderbird; wonky meaning that I got an error message when I tried to log in, and then, when that resolved, couldn't send from webmail. Was only for a short time, then it resolved, but the problem with Thunderbird persisted. Optus are in the process of 'improving' their email platform, apparently, so maybe that's the culprit!

Gday Sue You are the third thread now but re > My partner, who also uses Thunderbird, cannot receive emails either. Do you mean send here???? Ie i also can receive and send via the webmail app i can receive to my PC but not send. My probs started Fri night 21 Nov, so its looking more ominous. As per my other thread, i have spoken to OPTUS several times they mentioned they have a lot of complaints re this but its not them :-(

Andrew

Gday Sue Just found this on the Whirlpool forums New settings that supposedly work

Server Name: mail.optusnet.com.au Port: 465 Authentication method: Normal password Connection Security: SSL/TLS

I just tried and you need to reboot TBird after setting On next send, you get asked for the password and then it sent??? See how longit lasts

Hi Andrew,

Sorry, yes, I did mean he cannot send, receiving is fine! :-D Interesting that your problems started about same time, and that Optus getting a lot of complaints about this issue. This website had a possible solution:

https://techsolvers.com.au/blog/how-to/cant-send-emails-from-optus-heres-the-fix/

But it's for Optus to 'unblock' the port, if that is the source of our troubles.

Gday Sue I replied earlier but it hasnt shown up Based on a current post in the whirlpool forums if you set security to SSL/TLS and port to 465 it will work. I tried it here and had to restart TBird after changing settings but i now appear to be able to send stuff Andrew

Thanks for that, Andrew. Unfortunately, I tried it, and restarted TB, but still did not send.

Gday Sue

Another thread by user FLIN just tried it and reports it works for him This is all way above my paygrade so see if yr partners machine works??? It might be something a bit more complicated than we have seen so far????? Andrew

Thanks, Andrew, that's great. I have tried those different ports but do not work for me. I will keep trying but waiting for Optus to get back to me also. Very frustrating.