Recently, we switched to using Postini's mail filtering services (now owned by Google) to improve our anti-spam solution and off-load the spam processing. Not that GFI wasnt doing a great job, I was just fed up of installing updates, managing the software and the additional load on the server.
Anyway, I digress. One of the issues we had, was some of our clients and vendors use a little more aggressive anti-spam methods and our mail wasn't being received. One of the culprits turned out to be my TXT=SPF record on the domains name server.
After a little more reading I was ready to make a new SPF record, but being the lazy guy I am, managed to find a wizard to do the heavy work for me.
If you are in the market for a new SPF record, check out the Microsoft "Sender ID Framework SPF Record Wizard". In four easy steps, the wizard will grab your current mx records, and help you build an SPF record. You can add additional outgoing domains and change the settings as you go.
This certainly made my life easier, and so far, seems to have solved the mail delivery issue.