As you can probably tell, there's nothing to suggest besides read the logs... there's just not enough info - how would the domain normally receive/process e-mails ... (presumably the server is still routing/sending them? To the correct place?) ... have there been any upgrades to software either at the server end or in the domain host?
To view text files in linux read the man pages for "more" and "less" and "cat" ... if the log files are archived, use "zless".
Usually you just use a text editor if you know where the log is ... how would he normally read these files and what went wrong with it?
If you want to help your freind submit a good question here, try getting a copy of the appropriate tutorial <
http://www.linuxquestions.org/questi...icle&artid=277>
to him.