I am currently having problems sending mail from my gmail account using Postbox (a Thunderbird variant) on my Mac. It worked until recently, and I can still receive mail.
I shouldn't think this is an issue with TalkTalk, which is the ISP my computer is connected to, but I suppose it is possible, but anyway maybe someone could help.
The error message I get is
Sending of the message failed.
The message could not be sent because the connection to Outgoing server (SMTP) smtp.gmail.com was lost in the middle of the transaction.
I can think of a couple of ways round it.
I could send from my TalkTalk account using my gmail address as a reply-to address. Trouble is that i am not sure that replies would automatically get sent there and not to TalkTalk, and also I would have to manually switch to my TalkTalk account even when I wanted things in gmail.
Alternatively, is there a way of telling TalkTalk that it is ok for them to send mail that uses my gmail address. I tried, and it didn't work, but it seems to me it should be possible, given that TalkTalk knows that I am the person connected to them.