Re: /usr/sbin/sendmail specification proposal, draft 5

["H. Peter Anvin" <hpa@transmeta.com>]

Daniel Quinlan wrote:
> 
> If you're saying that we shouldn't limit applications to only the above
> two options (SMTP over SSL being another option), then I agree.
> 
> I meant to say that LSB applications must deliver mail by
> 
>   a) using /usr/sbin/sendmail
> 
>   OR
> 
>   b) support SMTP over TCP on server port 25 to the local host;
>      support SMTP over TCP on server port 25 to a remote host
> 
> So, it would *not* be sufficient for LSB compliance to support *only*
> SMTP over SSL.
> 
> To rephrase things a bit:
> 
>      To deliver electronic mail (email), applications shall use either
>      the interface provided by /usr/sbin/sendmail (described here) or
>      an internet protocol such as SMTP (RFC 821).  If an application
>      is unable to deliver mail via the /usr/sbin/sendmail interface,
>      then it shall minimally support using SMTP over TCP connecting to
>      port 25 of either the local host or a remote host.
> 
> I'm considering dropping the last sentence entirely.  The point was to
> require applications to use /usr/sbin/sendmail instead of mail or
> mailx.  I'm not sure I want to go too far beyond that.
> 

My point is that talking SMTP to a remote host -- to port 25 or any
other port -- is completely unstandardizable, since it would require the
host to talk to to be specified system-wide.  At that point you could
also specify a port other than SMTP, or a transport mechanism other than
TCP (such as SSL.)  Right now, there is no way to do that, so it would
require either a new interface to be invented which noone currently
supports, or it is not appropriate for standardization.

Therefore, there are only two standardizable interfaces:

	* /usr/sbin/sendmail
	* SMTP to port 25 on localhost

We may want to specify the latter as the port returned by
getservbyname("smtp","tcp") rather than specify the port number in the
standard.  On the other hand, that is likely to break some programs, so
we may want to specify that getservbyname("smtp","tcp") shall specify
port 25.

Also, IMO /usr/sbin/sendmail should be preferred if it exists, and that
should be noted.  Otherwise, mail would be completely broken on
non-TCP/IP systems, if any still exist.

	-hpa