During a mail merge, how to send a single email to a user instead of multiple ones?

Question

I have a table that looks somewhat like this:

User Email   |   Invoice Number   |   Company
  [e-mail]             12                 xyz
  [e-mail]   |         13         |        yyy
  [e-mail]   |         112        |       add

When I do mail merge, I do a merge field on invoice number and company and send it to the user's email. This results in [e-mail] getting 2 emails for 2 different invoices; is there a way to automatically send 1 email instead?

A current solution I have is to have multiple 'invoice number' columns and transpose the column based on the user's email, however that way I lose information on which company the invoice belongs to. Is there a better way?