On 13 Feb 99, at 0:23, Winship <[log in to unmask]> wrote:

> I know that in some systems mail can be truncated because the system
> interprets a period (.) in the fist column as an end of file flag.
> Can the same thing happen with an underline (_) in the first col?
>
> Douglas
It is singular to a single dot on a line of its own, and has to do with the
fact that some of the mail servers are compatible with the Internet
standards only partially.
It is not a problem with LISTSERV, but rather with the mail transfer
agents at the side of some subscribers, the problem does not exist with
underscore.
On SMTP each mail message is "enveloped" with the SMTP commands
for posting it - this is called "the SMTP envelope". Acorrding to SMTP
standards (RFC821) each BODY of a message is ended with the
combination "<cr>.<cr>" (without the quotes) which means a dot on a
line of its own, and this tells the SMTP server that now the transfer of
the message body is finished.

Now you may address a question: "So how a mailer should handle a
<cr><dot><cr> if it appears in the body of the message?", and RFC821
also address this question, by instructing that the server of the sender
to replace this combination with another one, and instructing the server
of the recipient to replace it back (By truncating all text to the right of a
period in column one). In some systems, this doesn't work correctly
along the way of the message, and the trasform back to <cr><dot><cr>
occurs to early. As a result the next server in the route understand the
combination as if the message body has ended, and ignores the rest of
the body as it can neither understand it as SMTP commands (security
hole?)

The problem is very clear in digested messages if one of the recipients
uses this combination in his signature

Uzi Paz