In my first startup, I switched our email from an ISP hosted offering to an self-hosted system. We were ramen poor, and this was projected to save us around $1K

In my first startup, I switched our email from an ISP hosted offering to an self-hosted system. We were ramen poor, and this was projected to save us around $1K/month. The replacement system was postfix with dovecot, worked like a champ. Got buyoff from CEO/CTO/CFO, deployed it; transitioned everyone over. One of the CEO's pet employees was pissed because of some problem with Mozilla/Firefox not working the way he liked. So the entire system was switched back, the very same day. Mail was messed up for a few days as we didn't control our DNS, and that was added to the blame game. Fun times. No matter how much buy-in you get, people can be unreasonable about making any accommodation for change.