internet mail
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... in message headers in a way which is unlikely to be disturbed by the
quirks of existing Internet mail handling programs. In particular,
some mail relaying programs are known to (a) delete some message
header fields ...
... headers, to "break" these programs would cause
severe operational problems for the Internet mail system. The
extensions described in this memo therefore do not rely on little-
used features of RFC 822std11(-> 2822prop) ...
... Borenstein N., and N. Freed, "MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1341(-> 1521(-> 2049draft | 2048(-> 4289 | 4288) | 2047draft | 2046draft | 2045draft)), Bellcore, Innosoft, June 1992. ...