"Cannot send email" error after posting a message

[geezmo]

SMF Version: SMF 1.1 RC2
After I've submitted a post, I got this message,

"Cannot send email to [email protected]"

I'm thinking this is related to a topic subscription by that poster. But this is not normal, and I know this occurred because my host did something with my server a while ago.

So my question is, can I solve this simply by re-uploading specific SMF files? If yes, which file/s? I don't want to reupload everything because I have a lot of modifications installed in the forum. If I knew which files need to be re-uploaded, then I can check whether that file has been edited because of mods and then I can do necessary changes

Or is this a host server problem and in that case how do you think I can solve it?