When I first came across Jilmail I was a bit relluctant to try it out because I felt something wasn't right. After a few Google searches, I discovered it was originally called WorldWide Messenger created by WorldWide Creations, who no longer exist. Although I never learned the whole story, it seems that Jilmail was a re-templated version of WWM, and was being sold cheaper, but I'd tracked down the download for free.
Either Jilmail gave WWM a run for their money or email scripts weren't going to make them their fortune, but eventually WorldWide Creations decided to give their email script away for free, to take the money out of Jilmail, so I ended up with both!
On top of that, WW Creations also gave away an instant messenger creator, which allows providers to style their own instant messenger for users to download, and an instant messenger server. I've never installed the instant messenger server so can't really comment, but will provide a link to the download shortly.
I tried installing Jilmail using the instructions provided but couldn't, then tried WWM but couldn't, then I combined the installation instructions to find it's quite easy really. Worldwide messenger has a basic layout similar to old yahoo style, with a full length header, a left hand column with email folders etc, and the main body for reading/writing emails. The script worked well but after a while I would get error messages when logging in, about duplicate entries, and the same hapened with Jilmail. It seems that messages are not deleted from the server once downloaded to the script, but they may be because of a duplicate database, one for Jilmail/WWM and the other for server emails.
Jilmail was much more presentable for the day, with a more stylish interface and better placed ad module.
In both, users could sign up for a free or fully featured paid account, and admin has full control over users accounts. Also in Jilmail was a template entitled 'old' which gave a different style altogether, quite comical really.
Unlike most other email scripts out there, even today, Jilmail/WWM povide a user registration page.
Both scripts are included here, and I've linked to the downloads together with the instant messenger server/creator.