Reasons behind defaulting atd and sendmail

[Les Mikesell]

Timothy Murphy wrote:

>>> But what has that got to do with desktops or laptops?
>> I think he meant to contrast desktops to servers.
> 
> OK, thanks.
> I often seem to mis-interpret the word "desktop",
> as eg in "desktop environment" or "desktop manager".
> It seems to be a word with several different meanings.

Yes, it could be used to indicate a program set (GUI, office 
productivity programs), or a single user machine that can be powered 
down at any time, or several other concepts that aren't always true. 
With Linux, any machine might be multi-user and/or running network 
services for others, and none of the programs necessarily run on the 
physical device that displays them (think ssh, remote X, or freenx/NX).

>> On desktops some people might prefer to configure their MUA(s) to speak
>> SMTP directly with an ISP or 3rd party relay, but the preference is more
>> likely due to the nicer fill-in-the-form configuration interface instead
>> of the overall functionality.
> 
> I must admit I'm rather ignorant in this area.
> Are you just saying you could use another program in place of sendmail?

You could (postfix is functionally equivalent), but what I meant was 
that sendmail could have a GUI config tool that took the same 
information as you provide a GUI MUA. It doesn't, and since it has so 
many options and a cryptic text config file, many users may not bother 
making it work in their situations.

> I understand that; but it is easy enough to turn off the sendmail service
> and start some other service, if that is what you want.

You can bypass it completely if you configure your MUA to use some other 
server and don't use any traditional unix style mail.

> Perhaps if you gave an explicit example of "speaking SMTP directly"
> I would understand better.

Modern MUA's have network POP/IMAP reception and STMP sending protocols 
built in.  You can configure those to work directly with any network 
target(s) you want.  In an office, that might be your company's mail 
server - at home it might be your ISP or 3rd party services like gmail. 
  Whenever you send or receive mail, the MUA will connect over the 
network to the configured server(s) without needing any local sendmail 
support.   However, in the traditional unix mail scheme, senders like 
cron, logwatch, and an assortment of other tools don't have individual 
configuration for mail delivery.  The old philosophy was 'one tool does 
one job well' and 'unix processes are cheap, start another one if you 
need it', so they just run sendmail and pipe the message to it for 
delivery.  Sendmail can be configured to do just about anything - the 
traditional unix scheme was to deliver to local mailbox files per user 
but it can just as easily forward everything to a server elsewhere.  The 
advantage of setting this up is that it is a system-wide service so 
besides working with unix tools, you can also let your MUA(s) use local 
sendmail as the transport so you only have to configure it once even if 
you use multiple MUA's or have multiple users or both.  When you use 
sendmail for delivery it will accept a message and queue it for delivery 
with automatic retries if it can't reach the relay immediately.  This 
may or may not be better than seeing it in your MUA's outbox until it is 
delivered at least to a reliable forwarding relay.

-- 
   Les Mikesell
    lesmikesell at gmail.com