SPF is a technique to prevent spammers from forging e-mail that says it originates from your domain. Once SPF records are published for your domain, SPF-compilant mail agents will be able to drop forged messages.
Let's say that your domain is mydomain.com. If you send a message that has a From address of <anything>@mydomain.com, that mail will now need to be sent through E-Intermart's servers. To do so, you will need to modify the settings for your outgoing mail in your mail client. Here are the settings that you will need to use:
SMTP Server: mail.e-intermart.com
Username: <Your standard POP3 username>
Password: <Your standard POP3 password>