The problem with delivery issues is you often don't know you have them ; I was paying for mail hosting to a small-ish hosting provider, and after 16 years of es

The problem with delivery issues is you often don't know you have them ; I was paying for mail hosting to a small-ish hosting provider, and after 16 years of essentially perfect service, I started realizing that gmail delivers ~25% of the mail I sent through them as spam - but not consistently. I spent hours trying to diagnose this, and so did the hosting service - to no avail, because we'd try something, a delivery worked ... and the next day, to a different recipient, it didn't - and it is sometimes hard to get feedback about those things. I really wanted to support the smallish hosting service - but I couldn't afford to lose so many deliveries. I sadly switched to FastMail and not a single mail that I know of was lost for a few years now. You say you are investing 2-4/year troubleshooting delivery issues; How do you know that the things you don't troubleshoot actually reach the receipient's inbox?