Yes, it is written in PHP. But, it's visually attractive.
My customer was having a problem with it. Messages were not being allowed to go to the net (they use some restrictions on which users can mail to Internet and which users can send internal messages).
I've found out that you can't leave the "domain" variable empty in config.php. The author probably used some bogus concatenation and the addres ends up as "user@.domain". If you don't put a FQDN there, it becomes "user@something_not_FQDN.domain.com". So, you HAVE to put your domain name there.
It sux. This should be left, IMHO, for the MTA.