Thanks @BasilDV, I've set up Thunderbird to use Gmail SMTP server with oAuth2 and now it works like a charm  :) ... View more

The issue happens with other email addresses on Thunderbird as well, not only with gmail. The exact same issue. So I think it's not related to gmail but to TPG and the way the communication is (not) established with TPG SMTP server.   FYI here are my settings:   Server name: mail.tpg.com.au Port: 587 Connection security: STARTTLS Auth method: Normal password Username: xxxxxxx@tpg.com.au   I've always been using these settings without any problem until very recently. Now I have the same issue as  Ascidian99 for ALL my emails addresses on Thunderbird (not only gmail). I can receive emails but I can't send them. Thanks in advance for your help. ... View more

Hi,   No. As I said I use a gmail address. ... View more

I have the exact same problem as Ascidian99 When trying to send an email it fails and I get the error "the mail server responded: mf-505: Sender Policy - Relay Denied". I use a gmail address with Thunderbird. I have the issue only with my gmail on Thunderbird. Proton mail works fine with Thunderbird. ... View more

Thanks a lot @david64  ... View more

Thank you. I will stick to Port 587 with STARTTLS as it works fine. I don't have any 'server requires secure connection' option on Thunderbird (see attached).   Is the password sent encrypted now that I chose STARTTLS? Anyway even in the case it's not encrypted when sent by Thunderbird, it will be encrypted when leaving my PC thanks to my VPN. ... View more

Fantastic! Using port 587 it works now  :) Thank you. Yes my VPN location is in Australia. But I tried using an oversea location, it works too, all good.   Just one question though: at the moment I use 'Normal password' as authentication method, is it safe? As I see I can also use 'Encrypted password' but when I do so I have the error: 'the outgoing server mail.tpg.com.au does not seem to support encrypted passwords'.   Thanks in advance for your help, much appreciated   ... View more