MX lookup
Lists the servers that receive mail for a domain, in the order senders try them, with the rest of its email records underneath.
The rest of the domain
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Reading MX records
Senders try the server with the lowest priority number first and fall back to the next one if it does not answer.
A domain with no MX record can still receive mail at its web server address, but many senders treat that as a sign the domain does not really use email.
A single MX record of . is a null MX: the domain is declaring that it accepts no mail at all.
Other checks
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