Hello,

Unixish systems have had a long history of having /usr/bin/sendmail available, which is probably why its existence is mandated in the LSB.

However, that requirement is really hard and not sensible to implement those days. Right now it means that whenever you install the "lsb" package on LSB conformant distributions, it pulls in a MTA, which is not something which is ever required if all you do is to install a printer driver from openprinting.org or an LSB-packaged Google earth, or whatever.

With today's spam filtering, running MTAs on random desktops simply does not work any more, at least not in the "classical" sense. So you have to set it up as a relaying MTA to your mail provider, but first that's heavily user unfriendly (because a lot of people don't know what all that means, are using web clients, or using MUAs which do the SMTPing themselves), and second it opens up a network port for an otherwise unused service, thus introducing a security attack vector.

Of course the current LSB does not actually explicitly say that /usr/bin/sendmail must actually be capable of sending mail to the outside world. That means that distros can (and do) configure e. g. postfix or exim to default to local delivery only, or shipping a minimal stub which just errors out or just does local delivery. However, that makes it more complicated than necessary to actually set up a real MTA. It also only fulfills the LSB to the letter, but not to the spirit. 

A crippled MTA is *much* worse than no MTA at all. In the former case, applications who see sendmail will just send mail into oblivion (few, if any, desktop users actually read /var/spool/mail), whereas in the latter case, applications see that an MTA isn't available and use a more appropriate means of communication.

Especially on desktop systems, applications shouln't expect to have local email delivery available, and most don't. Distro packages which do have to depend on an MTA anyway, and LSB packages should just check if /usr/bin/sendmail is available instead of blindly assuming that they can send mail to anywhere without any configuration and no error handling.

So in summary, the LSB should continue to define the behaviour or /usr/bin/sendmail, but not mandate that it is available on all systems (especially not on desktops).