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I would like to know what is the pop3 and IMAP server used in zimbra .. As I was looking out for a pop3 and IMAP server that can recognize virtual domains.
The POP and IMAP servers are built directly into the ZCS server. We do not use a third-party POP/IMAP server.
The ZCS POP/IMAP servers are scheduled to have virtual domain support for the 5.0 release. Please check the relevant bugzilla entry (Bug 16184 - RFE: POP3/IMAP Virtual Domains) to keep tabs on progress.
Bugzilla
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POP3 Server 
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