RFC 3958:Domain-Based Application Service Location...
RFC-Ref

IMAP4


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... application-layer protocols (e.g., POP3, IMAP4). A tag, such as "RetMail", could be registered for it. (Note that this has not been done, and there are no plans to do so at ...
... IANA-registered tags. Using the mail example above, "POP3" and "IMAP4" could be registered as application protocol tags ...



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