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.
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 issues are not discussed in this memo.
 Myers, J., and M. Rose, "Post Office Protocol - Version 3", STD 53, RFC 1939, May 1996.
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