What is the POP/IMAP CAPAbility command?

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Answer

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

  • TOP
  • USER
  • PIPELINING
  • RESP-CODES
  • UIDL

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

  • IMAP4
  • IMAP4rev1
  • LOGIN-REFERRALS
  • ACL

Keywords:POP3 IMAP4 capability

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