Mitel_ephone,
I am not sure how much you know about SMTP, but you are getting an error code 334 which means it is an authentication error when trying to connect to the server. My suggestion, without more information to go on, would be to clear out your username and password under the E-Mail Gateway and put them back in correctly as they may have been corrupted during the upgrade. When you see 334 VXNlcm5hbWU6 [Username] it is using Base64 and is requesting a Username and it either isn't getting a good one or it isn't getting one at all. By the way if you get 334 UGFzc3dvcmQ6 [Password] that means your username is good and it is now requesting a password. Hopefully that helps a little, if you need more help just post back here and I will check in every so often tonight.
Thanks,
TE