right click in the group member list, select to sort the members.
In the resulting window, select to sort them by company (or whatever field you prefer) and enter this in the 'reference text' box:
Wait for the members to sort.
You'll now have an e-mail address (or not) in the reference column for each group member. You can click the reference column header to sort the list by the reference. This should put all the blank ones together. Click on the member at the top of the list who has a blank in the reference column and shift-click on the last member with a blank in the reference column. This should highlight all of those who have no e-mail address. You can then right-click on that highlighted mass of members and select 'Delete...' After confirming, you'll have removed them from the group.
Thanks Doug this is really a great tip about Groups management.
It save us a lot of trouble and save me to deeply study SQL...
Sure, I could probably write the SQL to do it, but when it can be done with the interface, why not?