    Network Working Group                                          R. Nelson
    Request for Comments: 1957                               Crynwr Software
    Updates: 1939                                                  June 1996
    Category: Informational

                     Some Observations on Implementations
                       of the Post Office Protocol (POP3)

    Status of this Memo

       This memo provides information for the Internet community. This memo
       does not specify an Internet standard of any kind. Distribution of
       this memo is unlimited.

    Observations

       Sometimes an implementation is mistaken for a standard.  POP3 servers
       and clients are no exception.  The widely-used UCB POP3 server,
       popper, which has been further developed by Qualcomm, always has
       additional information following the status indicator.  So, the
       status indicator always has a space following it.  Two POP3 clients
       have been observed to expect that space, and fail when it has not
       been found.  The RFC does not require the space, hence this memo.
       These clients are the freely copyable Unix "popclient" and the
       proprietary "netApp Systems Internet Series".  The authors of both of
       these have been contacted, and new releases will not expect the
       space, but old versions should be supported.

       In addition, two popular clients require optional parts of the RFC.
       Netscape requires UIDL, and Eudora requires TOP.

       The optional APOP authentication command has not achieved wide
       penetration yet.  Newer versions of the Qualcomm POP server implement
       it.  Known client implementations of APOP include GNU Emacs VM client
       and Eudora Lite and Eudora Pro.

    Security Considerations

       Security issues are not discussed in this memo.

    References

       [1]  Myers, J., and M. Rose, "Post Office Protocol - Version 3",
            STD 53, RFC 1939, May 1996.

    Nelson                       Informational                      [Page 1]

    RFC 1957             Notes on POP3 Implementations             June 1996

    Author's Address

       Russell Nelson
       Crynwr Software
       521 Pleasant Valley Rd.
       Potsdam, NY 13676

       Phone: +1.315.268.1925
       FAX:   +1.315.268.9201
       EMail: nelson@crynwr.com

    Nelson                       Informational                      [Page 2]