This page describes RFC's which are relevant to hMailServer.


  • RFC 5321 - Simple Mail Transfer Protocol, SMTP
  • RFC 3501 - Internet Message Access Protocol, IMAP, v4
  • RFC 1939 - Post Office Protocol, POP, v3

Message encoding

  • RFC 2047 - MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text
    • RFC 2045 describes a mechanism for denoting textual body parts which are coded in various character sets, as well as methods for encoding such body parts as sequences of printable US-ASCII characters.  This memo describes similar techniques to allow the encoding of non-ASCII text in various portions of a RFC 822 [2] message header, in a manner which is unlikely to confuse existing message handling software.
  • RFC 2184 - MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations
    • a means to specify parameter values in character sets other than US-ASCII
    • to specify the language to be used should the value be displayed, and
    • a continuation mechanism for long parameter values to avoid problems with header line wrapping.

IMAP extensions

  • RFC 2177 - IMAP4 IDLE command
    This command allows IMAP servers to notify connected clients when a new message has arrived (rather than having the clients poll for new messages).
  • RFC 4314 - IMAP4 Access Control List
    This extension is used to create public folders shared among several folders. The document specifies for example how access is granted by an IMAP client.
  • RFC 2087 - IMAP Quota extension
    With this extension, IMAP cients can check how much of their server disk quota has been used and how much is available.
  • RFC 5256 - SORT and THREAD Extensions
    The SORT extension provides server side sorting capabilities. This adds performance, since IMAP clients does not have to download all messages in a mailbox to be able to sort them. The Thread extension is not implemented in hMailServer.


  • RFC 4871 - DKIM specification
    DomainKeys Identified Mail (DKIM) defines a domain-level authentication framework for email using public-key cryptography and key server technology to permit verification of the source and contents of messages by either Mail Transfer Agents (MTAs) or Mail User Agents (MUAs).


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