Thank you very much for the additional context. On 2013-05-08, at 9:40 PM, Ben Morrow <b...@morrow.me.uk> wrote:
> At 4AM +0000 on 9/05/13 you (Earles, Jill) wrote: >> Wow, that is a lot of detail. Thank you very much. I appreciate the >> Unix security perspective - that's something I'm trying to learn more >> about and be more in tune with as a new systems administrator. >> >> We are not using dotlocks, and the adduser command does create all the >> mailbox files with the correct ownership automatically. >> >> I don't know what MTA or MDA are. > > These are standard mail jargon, so you'll probably come across them > again. MTA is Mail Transfer Agent, that is, the program which receives > incoming mail (usually by SMTP) and decides what to do with it. > Traditionally on Unix this was Sendmail; nowadays it might be Postfix or > Exim or something instead. > > MDA is Mail Delivery Agent, and it's the program the MTA hands a mail to > when it decides to deliver it to a local user. (You may also see LDA, > Local Delivery Agent, used for the same thing.) Traditionally this was > often mail(1) or something equally unsuitable; nowadays it might be > procmail or maildrop or something else. Dovecot provides an MDA called > 'deliver' or 'dovecot-lda' (they're the same program) which it's often > worth using if you haven't got a good reason not to. > > Other terms are: MUA, Mail User Agent, which is a program users use to > read mail; and MSA, Mail Submission Agent, which is the program users > use to submit new mail for delivery; traditionally this was sendmail(8), > but now it's more usual to have a special-purpose SMTP server, often > running on port 587. (Users should not submit mail directly to MX SMTP > servers, because generally mail needs to be cleaned up before being sent > off-site.) > > From the point-of-view of the mail system, a POP/IMAP server like > Dovecot is considered part of the MUA, the other part being the user's > actual client; this arrangement, and the corresponding actual- > client/submission-server split for outgoing mail, is often called > 'split-client'. > > Ben >