[haus]

From the link: "You may be utilizing a dynamic IP address which was previously utilized by a known spammer."

The Sprint IP address you had while connecting to your corporate SMTP server is on the RBL. Here's the thing...when you're using authenticated SMTP, RBL checks should be bypassed because authenticated SMTP is designed to provide you with credentials. So my guess, based on not a lot of detailed info, is that your mail system is misconfigured to continue using the RBL despite your authentication.

Unfortunately diagnosing email problems can be quite a challenge. You could try turning your phone off for a few minutes, then back on, and see if you get a different IP address (maybe you got an unlucky address and the whole netblock isn't in the RBL). DCHP leases are sometimes sticky, so maybe when you reset your phone you got assigned to a new block that's in the RBL...worth a shot.

Bottom line, though, when you're authenticated, you should be allowed to send from any network.