Hopefully someday the new horde/imp will be ready. Here are some shots of the CVS version I have on my old 5.1.2 box. CVS as of a few days ago....
http://82camaro.netfirms.com/horde_cvs.htmSome of the added features I like:
short previews in the inbox(you can change the size, turn them on for only new messages or all messages, etc...)
forward from the inbox
mark messages as important(or anything else) while you view them.
create html email(haven't messed with it much)
improved menu bar
'report as spam' will send it to spamassassin
it's own fetchmail(it can pull email from any number of pop/imap accounts--at login or on demand)
administration via the web interface
shared calendars, tasks, etc...
invite people to an event (calendar) It sends an email with a 'special' attachment that auto-adds the event to their calandar upon clicking it.
file manager (ftp client)
many selectable themes ("the one shown is blue and white")
It will be a nice webmail system once it's all done. Hopefully it will then be integrated with SME. It does require some additional php stuff 4.2 is the minimum, domxml, ctype to name a couple. The amount of modules is huge, I don't have 1/3 of them on my CVS version.
The released version of IMP is pretty good, especially if you add the calendar, tasks, and vacation to it(all we use here is Horde/Imp for email).
Ismail is alright if you must have the 'outlook' look to it. You may also look at atmail.com. With IE6 it even has drop down menus...looks very much like outlook express. Our users got used to not seeing all the folders all the time and having them available with a simple drop down menu. They really like the power of the expand names addressbook search--getting the addresses they need without opening up an additional window.