I will always recommend against running your own mail infrastructure. The administrative expense is to high in the long run. Unless you want to employ a 24/7 on-call admin team, Office365 is always the better choice. Email encryption can still be done client side (SMIME/PGP).
"running your own mail infrastructure" - I once got responsibility for a complex email nightmare dumped on me (tens of thousands of users, hundreds of domains, hundreds of servers) and I had no idea the vast number of entertaining ways email infrastructure can be screwed up.
Mind you - I guess at a small scale it might be OK - but infrastructure like email is both vital and utterly thankless. Let someone else do it.....
Still have nightmares from my first job in help desk, sweating bullets while handling decades of Outlook .pst files for a C-level in my company. Only place they existed were on the laptop itself, and a cheap 250GB external drive.
I still remember the conversation with a senior IT support guy who had been sent my way by the CIO - "<boss> says to speak to you as email is broken". "How much of it is broken?", "All of it"....
The cheap VM running sendmail with 12,000 entries in its alias file was being DOSed....
That was my introduction to crappy large email systems!
I asked them that directly (it was a tiny company and I was like 20) and the answer was no, but that they wanted to hold onto them in the event they needed to look up old contract info.
Looking back, I should have suggested backing it up to network storage. I imagine it must have been stressful traveling or going through TSA and worrying about losing 20 years of email data.
I agree that one should not host their own mail server these days, however, do the business, clients, and employees a favor and evaluate something in other than Outlook and Exchange based email systems.
I've been running email servers for my personal and business email for nigh on two decades now. It's "an hour or two of maintenance a quarter", on average, and is nowhere near as big of a deal as many would make it out to be. Is it 100% perfect? Certainly not. Would it be 'easier' (FSVO) to just give my email to gmail/O365/fastmail? Probably. However, I feel "the net" was meant to be (and works best as) a series of decentralized systems. Feeding my data into a 'just this side of a walled-garden' ecosystem does not help the net, so I don't do it.
I agree, there are tons of good options out there, such as ProtonMail or others. As a sysadmin, who no longer works in the MSP world, managing Exchange was such a huge time-sink. There is reason basically every MSP who is worth their salt will migrate their clients to O365 or some other solution. It works. There is relatively little down time. And you barely have to manage it. It's a win-win for everyone.
I will always recommend against running your own mail infrastructure. The administrative expense is to high in the long run. Unless you want to employ a 24/7 on-call admin team, Office365 is always the better choice. Email encryption can still be done client side (SMIME/PGP).