I presume you mean Customers, not Vendors since you are referring to SO-F.  The Auto-email option means that if you are emailing a batch of invoices, it will automatically send them rather than you having to click Send for each one.  If you choose contact Name, then it will match the "Attention"  contact name of each invoice with an email address in AR-A and not email those with no email entered.  if you choose a contact number then it will send to the email address of that contact number regardless of the "Attention" name on the sames order.  In any case, it only applies to the batch of invoices you are printing.
 
To answer your question, you could enter the email address for customers who want emailed invoices onto line 5 and then choose auto email and Contact 5 and only those invoices will be emailed.  However, the program logic to "print" (and assign invoice number and mark as printed) will apply to all released sales orders in the range.

the US-A program is T7SMK.RWN   and yes you have to set it up per user and per company if you have multi companies.