> At least, by running your own email instance, it gives you the ability to easily debug what the problem is with direct logs.

You really really should not need to be doing this yourself. I've had to fix a few of those and it's REALLY not worth anyone's time.

Getting email from Google is $6/mo, Microsoft $6/mo, Zoho $1/mo, Proton $4/mo, Fastmail $3/mo, etc.

Then it's just set it and forget. You don't have to track down quarantined messages, cross-examine a bunch of headers, check blacklists and whitelists, figure out how your SPF is propagating, blah blah blah... it's just not a wise thing to skimp on.

Do you really want your startup employees to be running into email problems while you're still trying to establish yourself as a business? At some huge corporate scale it might make sense to in-house this again (and even then it's questionable), but it's certainly not worth having a dedicated person (or generalist IT scapegoat) waste time setting this up and debugging it in a small or medium-sized business.