Some ISPs (Internet Service Providers) will block sending mail on the default port 25. Follow the Steps Below to take you through changing your port to 587 which will allow mail to be sent.
1. In the Mail app, swipe from the right-hand bezel of the display towards the centre to bring up the Charms bar, and tap Settings at the bottom.
2. Underneath Settings, tap Accounts.
3. Underneath Accounts, tap The account you want to amend the port for.
4. Scroll Down until you come to Server Settings and update you’re the outgoing server port to 587.
5. Click the Back button in the settings tab to save the changes