I have searched all of the forums where this same question has been asked with no real definitive answer at all.

I have tried all of the suggestions, none of them work.

I have had Outlook on my MacBook for 2 years with no issues, all of a sudden I can't send emails!

The strange thing is after messing about with settings and restarting the mac it did work again for a while (using the original settings) then all of a sudden the issue returns.

If I connect to a different network (my neighbours wireless) then it sends fine, so the settings must be correct surely?

It has to be an issue with Outlook - I have spoken to my ISP (Virgin) and Domain hosting ISP who both say my settings are correct, no misspellings or added spaces that can't be seen, as I say it works on another network!

Will someone please try to explain what is going on.