Setting up an IMAP/POP proxy server is useful for larger Zimbra Collaboration Server sites that want to present a single hostname for POP/IMAP. Enabling IMAP/POP proxy servers allows mail retrieval for a domain to be split across multiple Zimbra serves on an account basis.
When the proxy server is configured, the default POP and IMAP ports are configured for the proxy server, and ZCS designates the Zimbra server port numbers. These port numbers cannot be changed. When you enable a proxy server on any Zimbra server, the servers that do not have the proxy server enabled must be configured with the same port numbers as those with a proxy server.
IMAP Proxy port - 143
IMAP SSL proxy port - 993
POP proxy port - 110
POP SSL proxy port - 995
IMAP server port - 7143
IMAP SSL server port - 7993
POP server port - 7110
POP SSL server port - 7995
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