CSF causing Mail Queue Timeout?

[spankymcgee]

As of about a week ago CSF appears to be timing out processing of queued emails. If the message is sent manually using WHM > Mail Queue it times out.
Nothing more specific than "connection timeout" is reported.
At the same time we started getting random calls from clients, their website wouldn't load for them, mail app can't connect etc.
We have flushed everything, restarted and enabled/re-enabled.

We have a client (dns&site) using ZOHO for their email, with CSF enabled, ZOHO starts deferring messages with a DOMAIN_NOT_RESOLVED error.

If we disable CSF the problems immediately disappear.

[spankymcgee]

It turns out that CSF was blocking the IP's being used for Resolver Configuration (WHM). The IP addresses had been changed by host support.
When the two IP addresses were added to CSF.allow and CSF.ignore everything went back to normal.

- Still not clear as to why the original Google IP's addresses were not being blocked by CSF without being added to CSF.allow/ignore.