Well, I'm guessing that you're using your iPad but it does help to know these things!
It appears to a problem with your SMTP server settings. At a guess, it's likely that you need to enable 'authentication':
Go to Settings > Mail, Contact, Calendars
Select your email account.
Scroll down to Outgoing Mail Server.
Click SMTP.
Change 'Authentication' from 'None' (which I suspect it currently is) to 'Password'.
That will hopefully work but you might need to change some other settings. If so, we'll need to know what comes after the @ symbol in your email address).