Update:
I tried to switch back to our SSL (TLS) server but received an error again.
I did schedule a reminder using the non-SSL settings and did receive the email reminder without issue. However, another one of my staff setup a reminder but still received the error message stating the message could not be sent.
The email has my email address as the "Server User" but has his email as the "From Address".
It should have his email address for both. This is why he is getting the error, because he is not authorized to send emails from my email address.
Why is method using my "Server User" for his reminder messages?
Your help is appreciated...
P.S. This is not a setup issue on our server, but rather an issue in how method is trying to send the emails.