What is the POP/IMAP CAPAbility command?
Both POP3 and IMAP4 servers can support a number of enhanced facilities. In order to discover which facilities are supported by a server POP3 uses the CAPA command and IMAP4 the CAPABILITY command.
The POP3 CAPA command returns a list of capabilities supported by the POP3 server. It is available in both the AUTHORIZATION and TRANSACTION states. A capability description MUST document in which states the capability is announced, and in which states the commands are valid.
POP3 supports the following enhanced facilities
The IMAP4 CAPABILITY command requests a listing of capabilities that the server supports. The server MUST send a single CAPABILITY response. This listing of capabilities is not dependent upon connection state or user. It is therefore not necessary to issue a CAPABILITY command more than once in a session.
IMAP4 supports the following enhanced facilities