More precise escalation rules
It would be nice to enhance the escalation rules of the support ticket system to require the tickets to meet more conditions.
For instance, the sender(client) address, the subject, or the message as well as a variety of ways to match it. This could be an exact match, not equals, contains, does not contain, starts with, ends with, etc.
This would work very well for me as I use one department strictly for purchasing products through the company. This way, everything is logged in the system and accessible on it rather than an email account. This is nice because it keeps everything together in one admin area, however I have to manually check everything and close the ones that don't need responses, such as order confirmations. I also use it if I need to contact a seller about a purchase, so I don't want those to be closed automatically. This is just my situation, however I'm sure others may also have their own way of usage.
Another option to consider in addition to that is if it is from a client, if an admin opened or responded to it and if so, how many times, and any other possible checks.
I know this isn't a huge need as some other features are which haven't been made, but if you find that this would be a good option to have in the long run to make WHMCS more customizable, please give this an upvote! I don't see any reason it should be declined, after all, you aren't forced to use it, it's just extra optional abilities.