In your Contacts app, you should have an option to create contact groups. Or you can create them online and they will sync to your phone.
Once you have your contacts organized into groups, AquaMail can do group emails to selected contact groups. Very easy. Here's how to do it in AquaMail...
When you start a new email at the left end of the 'To' field tap on the little people icon.
Your contacts list pops up and across the top is 3 choices - Contacts (the default) Groups and Recent.
Tap on Groups, select a group and everyone in that group is added. You can deselect individually anyone you don't want the email to be sent. You can even select multiple groups.
No doubt some other ther email clients are able to do this also. But AquaMail is my favorite and one I'm certain is capable of group emails. IMHO AquaMail is one of the best apps available for Android. Top quality software.
https://play.google.com/store/apps/details?id=org.kman.AquaMail