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A Microsoft 365 administrator is troubleshooting mail flow issues for a custom domain 'contoso.com' after migrating to Exchange Online. Users are able to send emails internally and receive emails from other Exchange Online users, but they are not receiving external emails. The administrator suspects a DNS record issue. Which DNS record should the administrator verify first?
- ACNAME record
- BMX record
- CTXT record
- DSRV record
Show answer & explanationAnswer & explanation
Correct answer: B. MX record
The MX (Mail Exchanger) record specifies the mail server responsible for accepting email messages on behalf of a domain. If external emails are not being received, the MX record is the most likely culprit as it directs incoming mail.
Why the other options are wrong
- A. CNAME records create aliases for domain names, not directly for email routing.
- C. TXT records are used for domain verification and SPF/DKIM, not for directing incoming email.
- D. SRV records are used for locating services, not primary mail routing.
DNS MX Record
The Mail Exchanger (MX) DNS record specifies the mail server that is responsible for accepting email messages on behalf of a recipient's domain name.
- Essential for receiving external emails.
- Must point to the correct Exchange Online endpoint for Microsoft 365.
- Priority values determine the order in which mail servers are tried.
Memory trick: MX marks the spot for your mail to arrive.