He's an hardware engineer, not a software engineer.

After many years of self-hosting an email server I also came to the realization that it's not worth the hassle (in terms of maintenance / problems) and I switched to Proton Mail.

Using a custom domain with Proton Mail is not free (and all the other alternatives I know of are the same) and there's little advantage other than having a nice name. I think for a HW Engineer this is good enough.

I wouldn't recommend self-hosting email to anyone, but the expense of paying Proton Mail is absolutely worth the peace of mind (you are in control of your email & can effortlessly switch email providers) and professional appearance.

We're talking about someone handing out $17/ea business cards here.