Symptoms

1. Cannot login to Horde. The following error appears in C:\\Parallels\\Plesk\ mp\\horde\\horde81.log :

   HORDE [error] [imp] FAILED LOGIN for test@domain.tld [123.123.123.12] to {localhost:110 [pop3/notls]} [pid 2380 on line 139 of "C:\\inetpub\\vhosts\\webmail\\horde\\imp\\lib\\Auth\\imp.php"]
   

2. Login to mail using command line fails as well :

   # telnet mail.domain.tld 110
   Trying 122.128.107.56...
   Connected tomail.domain.tld.
   Escape character is '^]'.
   +OK Welcome to MailEnable POP3 Server
   user test@domain.tld
   +OK
   pass  1XXXXXXXXX
   -ERR Unable to log on
   

Cause

Password for mail account in Mailenable is not synchronized with mail password in Plesk database.

Resolution

Update password for mail account in Plesk Control Panel->domains->domain.tld->Mail accounts ->mail account.