The "Mailbox is locked by POP server" problem

Cyrus-imapd commonly reports “Mailbox is locked by POP server” when more than one POP3 connection attempts to retrieve email for the same user simultaneously. In other words, one computer is retrieving email over POP3 and has not finished when another computer connects. The later connection is rejected by the POP server with “Mailbox is locked by POP server”. Possible causes include network problems or a user’s computer failing to finish receiving mail and opening a new connection to try again. This is not a cyrus-imapd bug. Its behavior follows the RFC standard for the POP3 protocol. The “Mailbox is locked by POP server” condition also prevents webmail (using IMAP) from deleting or moving messages or changing their status because the mailbox is locked. Zimbra Mail Server installation service