SMTP stands for Simple Mail Transfer Protocol and is one of the more common means these days of sending/receiving mail messages.
127.0.0.1 is a unique and special internal network address that can only refer to the host machine.
I notice though that the error message goes on to specify a problem with php.ini and refers to port 25. These are normally specified by the installer of the php scripting interpreter on the machine hosting websites. I'd still say that this is a hosting company error and probably only they can fix it - especially as Martin said in one of his messages that the entire server had been hacked.
What's puzzling is that posting messages to a message forum has absolutely no interaction with sending mail messages, unless the poster has specific mail requests selected.
Obviously, from the comments above, that's not the case, so why is the action of posting a message trying to access the mail server?
I'm wondering if there's still a nasty piece of code running somewhere that's attempting to post user account details to some unknown address. Maybe it wan't a simple 'nasty message' hack, but one which also planted some code?
I'm guessing the webhost would have checked for this, but maybe not.