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I think it's because this email address does not conform to the standards in https://en.wikipedia.org/wiki/Email_address
The domain name part of an email address has to conform to strict guidelines: it must match the requirements for a hostname, a list of dot-separated DNS labels, each label being limited to a length of 63 characters and consisting of::§2
- uppercase and lowercase Latin letters
9, provided that top-level domain names are not all-numeric;
-, provided that it is not the first or last character.
In your case, the domain is all-numeric, which likely is the reason that these addresses are invalidated.