I ran my own mail servers for years. I switched to mail-in-a-box (MiaB) about 2 years ago and I don't regret it any single day.
Sure, it helps to know mail protocols and implementations inside-out, but... What does it help really? I was a ISP admin and then I had to know it. Now I don't care any more.
But back to what is really important: MiaB is a fully functional and *well* maintained solution that automate its maintenance. If it's not your job and/or you're not dedicating some non trivial resources to just be aware of what's happening in that knowledge space, you'll never be as good as a well maintained solution.