Hi Scallywag,
I know you say you checked all the settings, but I have been caught out before setting up a new ISP and when I checked and rechecked, I had missread the line with SMTP in it.
I had SMPT........it is one of those "what you want to see, you do".
Go, OE/tools/accounts/mail/properties/mail
and then check that SMTP line !
More later.