I tested merge to email before running a larger mail merge and was not
prompted to confirm each email. However, when I ran the large mail merge I
had to confirm each email.

Is this because some of the addresses are outside the company and/or the
main document and datasource were created by someone else other than the
final sender of the email?

I would prefer not to use third party software to avoid this.

Thanks for at least an answer as to why this occurred the second time but
not during my test.