Smtp, smtp cr, smtp crlf, smtp crorlf, smtp lf, nosmtp, lmtp, lmtp cr, lmtp crlf, lmtp crorlf, lmtp lf Channel Options

Channel protocol selection
These channel options specify whether or not a channel supports the SMTP protocol (or LMTP protocol) and what type of SMTP line terminator (or LMTP line terminator) the MTA expects to see as part of that protocol. means that the channel doesn&#x27;t support either SMTP or LMTP; all the rest of these channel options imply either SMTP or LMTP support.

The selection of whether or not to use the SMTP or LMTP protocol is implicit for most channels; the correct protocol is chosen by the use of the appropriate channel program or programs.

The channel option ---or one of the   variants---should be set explicitly on all SMTP channels;  but if no such option is set on a   channel, the channel will default to. The channel option ---or one of the   variants---is mandatory for all LMTP channels.

The channel options,  ,  , and   may be used on SMTP channels to specify what character sequences to accept as line terminators. or  means that lines must be terminated with a carriage return (CR) line feed (LF) sequence. means that lines may be terminated with any of a carriage return (CR), or a line feed (LF) sequence, or a full CRLF. (Note that prior to MS 6.0,  used to be synonymous with , rather than with   as currently; this change to a more strict insistence on proper SMTP line terminators was made in accordance with RFC 2821.)   means that a LF without a preceding CR will be accepted. Finally,  means that a CR will be accepted without a following LF. It is normal to use CRLF sequences as the SMTP line terminator, and this is what the MTA itself always generates; this option only affects the MTA&#x27;s handling of incoming material.

The  channel options are similar, applying to the LMTP protocol rather than the SMTP protocol.

Note that the setting of the original, "default" incoming TCP/IP channel is what controls the behavior for all incoming TCP/IP channels to which that channel may subsequently "switch". That is, subsequent "switching" (due, for instance, to,   ,  , or    sorts of effects) will not result in a change of SMTP line terminator regardless of what may be set on that "switched to" channel; the option specified on the original incoming  TCP/IP channel (typically  ) stays in effect.

See also:
 * LMTP channels
 * TCPIP channels
 * switchchannel Option
 * saslswitchchannel Option
 * tlsswitchchannel Option
 * SMTP and LMTP protocol channel options
 * Channel options