How can we improve WHMCS?

Mine is not a huge user base - it's mainly boutique hosting for clients, so I have to be able to be selective in some cases with regard to mass email. An attempt to send an email to all clients with hosting services is easily done through the Mass Email tool, but there is no way to deselect one or more clients from the list.

Conversely, when selecting through Clients>Products/Services>Shared Hosting, while I can be selective and even perform additional selective filtering, I can only do this on a single page at a time. If the list extends to the next page, all previous selections are lost.

Additionally, once in the "send email" part, there is no way to batch them so they don't all send at once, nor will it filter duplicates as the mass email tool does.

If those Mass Email options could be added to the above process, that would be helpful, but perhaps a better option would be to make the Mass Email tool with just a little more filtering added in order to be a little more detailed in selecting.

If a user base was in the thousands or hundreds, I can see where it would be unwieldy if a list of clients was produced to deselect on the Criteria selection page, so maybe an exclusion filter - by client ID or email address.