Options for allowing external senders to avoid greylisting and other checks

Hi, So I have migrated my clients to a new cpanel server and have took the opportunity to dive in and enable greylisting across the board. Straight away a client's supplier is using a bespoke system that hasn't been coded well and gives up trying to send mail when deferred. I have seen the trusted hosts list but it is IP only and I am wondering where else I can put a single email address or whole domain and have it bypass greylisting. Related second question I seem to have lots and lots of places to "whitelist" or "allow" domains, email addresses and IPs and am kind of losing track now where each one is and when you would choose it over another option. Is there a list where all these places are within cpanel and what they whitelist against. It would save me a lot of time rather than having to dig through documentation per feature one at a time, the rub being I forget what feature contains which whitelist option. Thanks.