Check out the SMTP proxy settings, and if you have SpamScreen give that a look too.
To answer your question directly, I do not know. I use WFS on a Firebox II with SpamScreen.
Oh yeah, review your default packet handling - since the upgrade are you "auto-banning" anyone???
If all else fails roll that thing back to the last flash image (you did save the previous flash, right???) and wait a week for a response from our WG buddies in Seattle lol....