Which email provider?

Whose SMTP are you using? If it's that provided by your ISP then it may well not work on another network. They may provide their SMTP for their own customers and only when connected via the ISP.

Incoming email generally doesn't have the same constraints, hence you still get use of your Inbox etc.

Hello Zenos, Thanks for response. My ISP is TalkTalk.net; POP3; I/C server mail.talktalk.net; O/G mail server smtp.talktalk.net. Is there a way to configure Thunderbird to send emails? Alternatively would changing from POP3 to IMAP on TalkTalk work.

POP and IMAP are all about incoming email, which I gather is working fine. What's giving you trouble is outgoing, which uses SMTP.

According to this page talktalk support authentication, which is necessary to be able to use the talktalk SMTP server regardless of your location or connection.

What this means is that your outgoing settings should have the relevant box ticked, and you should fill in your usual talktalk login and its password, same as you use on the incoming settings.

In Tools|Account Settings go down the list of accounts and the last one, "Outgoing Server (SMTP)" will let you see your outgoing settings.

Thanks Zenos, I have now set Authentication to Encrypted Password. Hopefully next time away that will resolve the problem.

Hello Zenos, Tried to send emails again on a secure site and with Encrypted Password in Authentication Method but still same result - T/B will not send emails except at home. Any suggestions to resolve this problem please!