That message almost always means the from address is invalid.
It may just be that the somebody messed with it on the MFP or the server, or that the server was updated and now requires a valid, instead of allowing a fake email account.
It can also occur when the authentication and from field don't match (If I login with my gmail account I can't send mail from yours for example)
And it may have been changed in one place and not another.
So, open CWIS and go to Properties .Connectivity > Setup > SMTP(Email) > Edit and confirm a valid email address here:
Then roll on to the SMTP Authentication tab and be sure it is identical in the Login fields too
And last, go to Properties > Services > Setup > From Field > Edit and verify it is the same here too. This one is the key when somebody changes in the other location, because this location gets filled in when the other location is setup originally, but it does not update after the other location gets changed. I have no idea why that is.
