suddenly can't send e-mails,only receive

Please verify, into your Thunderbird account setting, the authentication method for smtp protocol

Open the Thunderbird menu Edit→Account Setting ... Outgoing server smtp

Select the defined server and then press "edit" button, change the authentication method, then retry to send the mail...

Hope this helps

When call your company for info, ask for the authentication method for smtp protocol... absolutely not need to tell them which mail user agent (Thunderbird) you are using.

Hth

Marco,
I checked with Bell on the authentication protocol and verified it is correct.Also tried changing the port to 587 but still no luck.Since Hotmail is working they said their server was not at fault and it must be Thunderbird.I see on the Thunderbird help that this appears to be a common complaint but none of the answers seem to fix the problem.Bell suggested I switch to Outlook Express but again some of the answers suggest that the same problem can exist.Any further thoughts on what my next step should be?Thanks for your help so far.John

Further to my problem,is it possible that the Ubuntu firewall sees this port(port 25 and/or 587) as a threat and is preventing it's use?Is there a way of telling the firewall that this port is acceptable or finding out if Ubuntu firewall has an acceptable port?

I switched to Evolution and can now both send and receive.Although this solved my immediate problem,the initial problem with Thunderbird still exists which doesn't speak highly of them.Crossing my fingers with Evolution.Thanks to Marco for his efforts.John