[BlueOnyx:18662] Re: SMTP Scheduled Delivery Time

[Michael Stauber]

Hi Darren,

> what is Delivery Schedule for?

When you look at the process list you will see something like this:

22374 ?        Ss     0:00 sendmail: Queue runner at 00:15:00 for
/var/spool/clientmqueue

The Sendmail Queue runner delivers email that are in the mailqueue. How
often it does that is defined by the "Delivery Schedule". Default is 15
minutes. When you change "Delivery Schedule" to something else (like 1
hour), then this will change accordingly.

"Immediate" in fact has little immediate effect as the queue-runner will
then switch to 15 minutes as a minimum.

But there is something else and that's the "Delivery Mode" of Sendmail.
These modes specify how quickly mail will be delivered when Sendmail is
asked to send something out:

    i deliver interactively (synchronously)
    b deliver in background (asynchronously)
    q queue only (don't deliver)
    d defer delivery attempts (don't deliver)

The old Cobalt RaQs used "q" for "queue only". In that case all mails
that Sendmail was supposed to send ended up in the queue and were then
delivered by the queue runner during it's next scheduled 15 or 30 minute
run.

When you selected "immediate" on a Cobalt RaQ, only then it switched to
"b" ("deliver in background") mode.

But keep in mind: The Cobalt RaQs had little horse power and slow I/Os.
So it made sense to let emails queue to conserve CPU cycles and to keep
the load down.

On BlueOnyx we switched to "b" ("deliver in background") pretty early on
as a standard mode of operation. This is actually the Sendmail default
and it will send your emails out immediately. But if that fails, the
emails go into the queue and are then scheduled for another delivery
attempt during the next queue run.

So if possible, emails will always be delivered immediately. If that
fails, the re-transmit will happen at intervals that you specify in the GUI.

For more info:
https://www.safaribooksonline.com/library/view/sendmail-4th-edition/9780596510299/ch24s09s35.html

-- 
With best regards

Michael Stauber