What is the difference between MnSMTP with other Mail Merge add-ons?
The MmSMTP has the ability to send emails via the SMTP protocol, so the amount of mail sent (daily) depends only on the sending server.
Is MmSMTP free?
The MmSMTP has a free version. Users are allowed to send 5000 free emails. Even when sending out these 5000 emails, users can still send at least 100 emails per day (not SMTP).