Proudly self-hosting since 2001. My mail server is in my basement. Do not know what you are talking about.
Means you're not using your email seriously. For example, to send CVs in response to job postings.
I send up to 20 email per day to people who have issues with their package build scripts, and I have no idea whether they ignore me because they stopped using the distro or because mail got dropped.
You should be able to see this on your DMARC dashboard