Thunderbird can receive emails but I cannot send them. I get the error message per the screenshot below concerning SMTP. I have a MacBook Air with Mac OS Sequoia 15.7.2. The error started yesterday (21 November). Just finished conversing with Optus support and they say that it's not at their end: webmail works okay, can receive email and send it (will note there was a brief hiccough earlier today when could not send from webmail, but okay now). All settings as recommended (port for incoming server actually different from what Optus recommends, but when I changed it from 995 to 110, Thunderbird stopped being able to download emails, so changed it back again. Port for outgoing is as recommended, 25.) I tried lowering security, as suggested by Thunderbird help list, and no change so restored it. I have the latest version of Thunderbird for Mac, 145.0. My partner, who also uses Thunderbird, cannot receive emails either. He has an older Mac running an older OS. I have included two images, the second one showing details of selected server. When I clicked 'fetch certificate' it failed. Does that signify anything important? The error console shows a lot of information, which of course I cannot understand, but can screenshot some of it if that would help. No firewall, no virus protection, no VPN. Any ideas as to what might be going on?