We are planning an Exchange upgrade next year. We are still in the early-planning stages, and have not decided on a version yet. We would probably just go with 2019. Also coming up for renewal is our public SAN cert that is used exclusively for email, so we may do all at once. all of our mail users are internal emp[loyees, generally using domain--joined computers (And we can deal with the exceptions to this rule as needed). Do we need to buy an expensive SAN certificate for mail delivery, or can we switch to a private certificate? I would need to know the answer for Exchange 2013, 2016, and 2019. I appreciate any help!