Not every domain that exists on the web is ready to receive email.
That is why domain and MX validation matter. A good-looking address can still bounce if the domain is not actually configured for mail.
The manual concept: MX records
Domains that receive email usually publish MX records in DNS.
You can check them manually with tools like:
dignslookup- web-based DNS lookup tools
If no usable MX records appear, that is a strong sign the domain is not set up to receive email.
Why this matters in list cleanup
If a domain cannot receive mail, every address on that domain is a bad send candidate.
That makes domain-level checks one of the highest-value filters in any validation workflow.
Manual checks vs list-scale checks
If you are checking one domain, manual lookup is fine.
If you are reviewing hundreds or thousands of addresses across many domains, you want the check folded into a proper list review workflow.
That is where MailCull helps. Domain and MX validation happen as part of the overall address review, so you do not need to inspect every domain one by one.