Network Working Group                                          R. NelsonRequest for Comments: 1957                               Crynwr SoftwareUpdates: 1939                                                  June 1996Category: 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 1996Author'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.comNelson                       Informational                      [Page 2]