He's already made up his mind, so he'll probably just leave out this important tidbit when discussing the issue with "management"

It’s certainly not free to arrange getting the new device, swap, reconfigure, and hopefully you have HA to avoid downtime.

It is an email server. You can set up some kind of system that “catches” incoming email while you take your hardware offline and replace it. Your internal users won’t be able to send or receive emails but anyone outside the organization would be none the wiser that your system was down. If you notify ahead of time and can keep downtime to under an hour, will it matter?

> certainly not free to arrange getting the new device, swap, reconfigure, and hopefully you have HA to avoid downtime

Compared to migrating to a new vendor?

Which you would need anyway if you switch to hardware from a different vendor.