On 2020-04-03, Caveman Al Toraboran <toraboracave...@protonmail.com> wrote:
> though i'm a bit curious about sendmail (if your > time allows). do you mean the ebuild "sendmail"? Yes. I meant the program provided by the "sendmail" ebuild. That is the MTA named "sendmail" that's been around since the universe cooled enough to form atoms: https://en.wikipedia.org/wiki/Sendmail For many years it was the de-facto standard MTA for Unix systems. It's very powerful but the configuration file format is almost impossible to understand, so people developed an m4 application that accepted a _slightly_ less cryptic language and generated the sendmail configuration file. At it's peak back in the early 90's there were approximately five people in the world who actually understood sendmail, and none of them ever worked where you did. The rest of us stumbled in the dark using the finely honed cargo-cult practices cutting and pasting random snippets out of example configurations to see what happened. Usually what happed is that mail was lost or flew around in a loop multiplying to the point where a disk parition filled up. That said, sendmail has features that no other MTA has. For example, it can transfer mail using all sorts of different protocols that nobody uses these days. Back in the 90's a number of replacement MTAs were developed such as qmail, postfix, exim, etc. When you installed one of these, (instead of the classic sendmail), they would usually provide an executable file named "sendmail" that accepted the same command line arguments and input format that the original did. That allowed applications who wanted to send email to remain ignorant about exactly what MTA was installed. Exim, postfix, qmail and the others were all still full-function MTAs intended for a multi-users system. They could route mail to different destinations (including delivering it locally to a variety of mailbox types) and accept inbound email from other MTAs. While they were far easier to set up and maintain than the original sendmail, they were still massive overkill for a computer that was used only by a single person where reading mail was done via POP/IMAP and all outbound mail was handed over to a single outside mail relay. They often didn't deal well with the fact that they were running on a host that didn't have a "real" hostname that meant anything to the outside world, and that the local hostname had nothing to do with the email addresses of the user(s). For that use case, simple MTAs like msmtp, ssmtp, and nullmailer were written that don't handle incoming mail at all, and where all outbound mail is sent to a single mail relay host. The first two don't even do any queuing: if you try to send mail when your relay host is unreachable, then the send simply fails. These too, when installed, provide an executable named "sendmail" that accepts the same command line options and input format as the original.
