Local copy of RFC 2821 segment that mentions Bare LF's in SMTP communications:


Klensin                     Standards Track                    [Page 32]
RFC 2821             Simple Mail Transfer Protocol            April 2001

4.1.1.4 DATA (DATA)

   ....

   The mail data is terminated by a line containing only a period, that
   is, the character sequence "<CRLF>.<CRLF>" (see section 4.5.2).  This
   is the end of mail data indication.  Note that the first <CRLF> of
   this terminating sequence is also the <CRLF> that ends the final line
   of the data (message text) or, if there was no data, ends the DATA
   command itself.  An extra <CRLF> MUST NOT be added, as that would
   cause an empty line to be added to the message.  The only exception
   to this rule would arise if the message body were passed to the
   originating SMTP-sender with a final "line" that did not end in
   <CRLF>; in that case, the originating SMTP system MUST either reject
   the message as invalid or add <CRLF> in order to have the receiving
   SMTP server recognize the "end of data" condition.

   The custom of accepting lines ending only in <LF>, as a concession to
   non-conforming behavior on the part of some UNIX systems, has proven
   to cause more interoperability problems than it solves, and SMTP
   server systems MUST NOT do this, even in the name of improved
   robustness.  In particular, the sequence "<LF>.<LF>" (bare line
   feeds, without carriage returns) MUST NOT be treated as equivalent to
   <CRLF>.<CRLF> as the end of mail data indication.

   ....


Now, check the 3com SMTP session:

[session start]
tcpserver: pid 18480 from 172.16.1.60
tcpserver: ok 18480 0:172.16.1.200:25 :172.16.1.60::2070
18480 > 220 mx1.server.com ESMTP^M
18480 < HELO [172.16.1.200]^M
18480 > 250 mx1.server.com^M
18480 < Mail From:<3com-sw@server.com>^M
18480 > 250 ok^M
18480 < RCPT TO:<admin@server.com>^M
18480 > 250 ok^M
18480 < DATA^M
18480 > 354 go ahead^M
18480 < From:3com-sw@server.com^M
18480 < Subject:Event from 3Com SuperStack 3^M
18480 < To:admin@server.com^M
18480 < cc:^M
18480 < ^M
18480 < From device 3Com SuperStack 3 (172.16.1.60):
18480 <
18480 < This is a generic test alert.
18480 <
18480 < ^M
18480 < .^M
18480 > 451 Bare LFs in SMTP check^M
tcpserver: end 18480 status 256
tcpserver: status: 1/50
18480 > [EOF]
[session end]