In 1.5.3 new E-mails doesn't appears when E-mail client is open, to see new E-mail, I have to reload RC. I don't know is it only my problem, but at all my Epesi instances there is the same problem.
I found that if I got message from Epesi user (same instance) system doesn't want to archive mail, it says that mail is already archived and looks like this is true, but massage remains in inbox folder and I can move it into archive only manually.
Time to time, some e-mails just impossible to open, I see mail in the list, but when I try to open it, at body I see just "Not logged". In cPanel RC webmail I can see and read same message, I opened new user in Epesi and that user can see and read mail, it inaccessible only for main account. I didn't find what cause that lock, it doesn't go often.