Re: [exim] delaying inbound messages

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Author: Phil Pennock
To: exim-users
Subject: Re: [exim] delaying inbound messages
On 2011-09-01 at 11:05 -0700, Jeff Lasman wrote:
>   # Accept hosts who are polite enough to wait rather than just send, as spammers do
>   accept hosts = *
>          delay = 3s

> Is there a community concensus on whether or no this is reasonable?

This is email. There's no community consensus on _anything_.

That said, I am one of those who does a delay, to expose the protocol
pumpers which don't synchronise correctly.

Make sure to whitelist your monitoring system. It's also handy to
whitelist all IPs configured on this host: @[]

What I do reduces down to:

  accept hosts = @[] : +remote_hosts_nodelay
  warn set acl_c_delay = 0
  # ...
  warn set acl_c_delay = ${eval10:3+$acl_c_delay}
  # add 2 seconds if on an RBL, etc etc
  # No delays at connect for submission, it's in the user-path:
  accept  condition = ${if =={$received_port}{587}}
  accept  hosts = *
          delay = ${acl_c_delay}s

together with a hostlist "remote_hosts_nodelay" which includes
+relay_from_hosts. The real ACL is more complex than that, because
that's how I roll.

Arguably, you might use a DNS reputation whitelist to reset the delay
down to zero before the end there.

You'll probably want to end up whitelisting the high-volume senders you
trust, if you want to keep them happy.