This makes me 😭
UPDATE: Thanks @[email protected] for this update: The issue has now been commented on and was closed by the maintainer, where they explained why those blocks would be nonsense. But it appears the OP wants to still talk with maintainer privately about it.
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It’s actually really easy to get past the custom domain issue.
If the domain is send-and-receive, it will need a SPF record to avoid getting blackholed by most mail providers. A TXT lookup for the SPF record would tie the custom domain back to the real provider.
Or even easier, you could look up the MX records to see what domain they point to.
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