Please explain -qq

Hi

My exim gets up to 80k emails submitted at once from a CRM.

I'm using

  queue_only_load = 2
  deliver_queue_load_max = 20
  remote_max_parallel = 10
  queue_run_max = 25

which means that when it's not under load (<2) emails are instantly 
delivered, but as soon as the load increases everything gets queued.

I am using -q10s to spin up queue runners to get processing the queue 
quickly. This worked OK, but is slow[er than I would like].

I read in the manual about -qq options, recommended for large queue 
workloads. However, exchanging -q10s for -qq10s resulted in no mail 
being sent!

I thought that -qq meant it passes over the queue once and kinda orders 
some stuff (does routing, defers remote hosts - that's all of the emails 
in my 80k workload - then can batch by recipient host) and then in a 2nd 
pass it delivers the mail, which it can do more efficiently thanks to 
the "hints" from the first pass. But it was like the 2nd pass never 
happened. I waited an hour; lots of processes appeared to be doing 
something, according to top, but whatever they were doing, it wasn't 
sending mail.

So I think I must have misunderstood what -qq does; perhaps it's not a 
substitute for -q? Do I need both?

Any tips for running a server to deliver lots of mail ASAP would be much 
appreciated, as would any explanation of -qq.

I'm running on Debian (so systemd). Exim 4.96.

thanks
rich

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