When is it ok to deliver email without an MX record?
Summary
What email marketers say9Marketer opinions
Email marketer from Namecheap explains that MX records direct email to a specific mail server. They are essential for receiving emails. If missing, email delivery is not guaranteed.
Email marketer from Hostinger answers that MX records are mandatory for receiving emails on your domain. They guide other mail servers to the correct destination.
Email marketer from Reddit shares that generally, if a domain lacks MX records, it implies the domain isn't configured to receive emails. Most mail servers rely on MX records to route emails correctly.
Email marketer from Email Geeks shares that it's also the default for many shared hosting providers if you register a domain with them.
Email marketer from DigitalOcean explains that MX records are crucial when configuring DNS. They are needed to ensure mail is routed to the correct server and can be received
Email marketer from ServerFault shares that delivering email to domains without MX records is problematic, but it may still work depending on the mail server's configuration. It's best to have an MX record configured for reliable email delivery.
Email marketer from Email Geeks shares that technically an A record can accept mail, but it's a strong indicator the domain doesn't handle mail.
Email marketer from ServerFault explains that it is possible to deliver email to an A record if no MX record exists, however it's not recommended as it's unreliable and can cause issues. It's also considered bad practice.
Email marketer from Email Geeks shares that it is possible to deliver email to A record as well, which is the main reason why people do not simply discard mails to domains without MX records and it is definitely an indication that mails may not be priority on that domain.
What the experts say5Expert opinions
Expert from Word to the Wise explains that MX records tell the world what servers handle mail for your domain. If you don't have them, other systems don't know where to deliver your mail.
Expert from Email Geeks explains that if there's no MX record, no A record but there is a AAAA record the delivery fails, because Fallback to A only exists at all because of backwards compatibility with the pre-MX record internet. AAAA is more recent than MX, so anyone who has a AAAA record knows they should have an MX record.
Expert from Email Geeks explains that if there’s no MX record but there is an A record you deliver to that.
Expert from Email Geeks shares it can also be a bulk-hosted vanity domain and that’s the main place I still see intentional delivery to A, less than there was, but still there.
Expert from Spam Resource explains that sending mail directly to hosts without MX records is allowed by the RFCs, but is not a good idea. It's inefficient because it requires mailers to look up A records for every delivery and doesn't allow for redundancy.
What the documentation says4Technical articles
Documentation from RFC 5321 explains that if no MX records are found, the mail server should treat the domain name as if it had an MX record pointing to the host itself, using the A record. However, this is a fallback mechanism.
Documentation from Microsoft explains that MX records are required for routing e-mail to your domain. They also specify the order in which mail servers should be used; a lower preference number indicates a higher priority.
Documentation from Cloudflare explains that MX records tell other mail servers where to send emails for your domain. If these aren't correctly setup, emails might bounce back to the sender.
Documentation from Google Workspace Admin Help explains that MX records specify the mail servers responsible for accepting email messages on behalf of your domain. Without these, emails might not be delivered.