Please recommend a trustworthy reference to troubleshoot custom domain settings
I have a custom domain which is set up for use with proton mail. I am on the proton mail plus plan. I get forwarded email from Gmail and I get emails sent directly to my custom domain addresses. So receiving works fine.
However there are a number of people who don't receive emails that I send from the custom domain email address. Others do.
I am looking for a reliable guide to troubleshoot my configuration.
Here is one example of the behavior I have observed, in case you like to think about problems, read on.
If I send an email from my custom domain to my Gmail account it will be forwarded from Gmail to the custom domain, but there is no sign of that original message in Gmail. Not in spam. Not in trash. Not in inbox.
I sent it there because I wanted to observe the headers and instead the above is what discovered.
The main problem is that I am sending emails that are not being received. I am technical enough to work this problem but I see a lot of conflicting information when I search the web, and a lot of folks selling a service to fix the problem.
Any insights are most welcome.
Thank you.