[whpalmer4]

No, you don't send to "--user@host" — you send to "user@host" and the subject line starts with "--" (or whatever you've configured in the OmniFocus preferences).

Or, sign up for a free gmail account and you can use the user+omnifocus@gmail approach. Ampsafe.com's mail server may not be configured to accept the "+omnifocus" format (it is optional).