Macbook air icloud mail account password verification

For months now mail on my macbook works absolutely fine until you try to send an email and then you get a continual 'can't connect to the account "mail"' message. I've resorted to using icloud mail in safari instead but I'm flipping well sick of it and would like to actually use the correct app! I clearly know the password because I've signed in here and in icloud but still it persists!

I've just removed the mail option from icloud settings and added it back and it's not made any distance. Would be interested in other peoples suggestions?!