SymptomsEvery account for every mailbox shows all messages as read when logging to mailbox through horde webmail.
CauseThe reason of the problem is that POP3 protocol, which is used for connection between horde and mail server, does not allow tagging messages as read all unread. This option is supported with IMAP protocol only; however default mail server (MailEnable Std) shipped with Plesk does not support IMAP protocol.
ResolutionIf you would like to use IMAP protocol it is necessary to install one of the following mail servers:
1. MailEnable Professional Edition.
2. MailEnable Enterprise Edition.
3. Merak Mail Server.
4. SmarterMail mail server.