Well, this could be the same problem as mine
(see "IMAP fixes provided by e-smith helpless?")
I hope e-smith support has read them and can do something - fixing it in next release would be fine

I believe it's a server-side problem, as I have tested 4 different e-mail client software on a total of 6 client PCs and they all behaved the same, but I do not use web-mail feature actually.
I would rather think it's IMAP-related. Of course, I'm not the one who can debug IMAP or analyze how it's implemented in e-smith as compared to the standard Red Hat...