TO AMEND YOUR SMTP PORT IN MICROSOFT WINDOWS MAIL
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.
Start Microsoft Windows Mail, select Tools » Accounts.
Highlight the account you want to change the outgoing port for and click properties
Select the Advanced Tab, Change the Out Going Server Port to 587 and click OK
You should now be able to send mail via our outgoing mail server smtp.iomartmail.com without being blocked by your ISP