My needs have changed a lot over the years. I no longer run company email for DayJob¹, and for the server I ran for myself, family & friends, I've jammed together a mail server³ from standard parts.
I still have Zimbra running behind a firewall (those who need access do so via SSH tunnel) for archive access, in case anything didn't transfer cleanly to the new arrangement and for things I didn't bother transferring.
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[1] since we've grown we have infrastructure/support people who look after that instead of muggins here doing everything, and we've long since² moved over to O365
[2] at least one buy-out ago
[3] the number of actual users⁴ is down to me and three others, and we barely used features beyond mail in the end
[4] more accounts used by those human users