Every email your domain sends or receives depends on a handful of DNS records working correctly behind the scenes. Three of the most important are the MX record, the A record, and rDNS (reverse DNS). Understanding what each one does makes it much easier to diagnose delivery problems or set up email for a new domain.
MX records: telling the internet where your mail goes
An MX (Mail Exchanger) record tells other mail servers which server should receive email for your domain. Without one, incoming mail has nowhere to go.
Each MX record includes two pieces of information: the hostname of a mail server, and a priority number. When multiple MX records exist for the same domain, sending servers try the lowest-numbered (highest-priority) one first, and only fall back to the next if that server is unreachable. For example:
yourdomain.com. MX 10 mail1.yourdomain.com. yourdomain.com. MX 20 mail2.yourdomain.com.
Here, mail1 would be tried first, and mail2 only used as a backup. If you use a hosted email provider, they'll usually give you the exact MX records to publish rather than asking you to build your own mail server setup.
A records: mapping names to addresses
An A record is the most fundamental DNS record type. It maps a hostname to an IPv4 address, which is how a domain name gets translated into the numeric address computers actually use to connect to a server. For instance, an A record for www.yourdomain.com pointing to your web server's IP address is what lets visitors reach your site by typing your domain name instead of a string of numbers.
A records matter for email too: the hostname referenced in your MX record typically needs its own A record so that sending servers can resolve it to an actual IP address to connect to.
rDNS (reverse DNS): confirming who's sending
While a regular DNS lookup turns a domain name into an IP address, reverse DNS does the opposite — it turns an IP address back into a hostname, using a special record type called a PTR record. When your server sends an outbound email, many receiving mail servers perform a reverse DNS lookup on your sending IP address to confirm it resolves to a legitimate, matching hostname.
If that lookup fails or returns nothing, the receiving server may reject the message outright or route it straight to spam, since missing rDNS is a common signal associated with spam sources.
One important distinction: unlike your website's A records or your domain's MX records, a PTR record isn't something you configure in your own domain's DNS zone. It belongs to whoever controls the IP address block your mail server sends from — in most cases, that's your hosting provider. If you're sending mail from an Avalon-hosted server and need a PTR record set or changed, that's a request for our support team rather than something you'd edit yourself.
How they work together
- A sender looks up your domain's MX record to find where to deliver mail.
- The MX hostname is resolved to an IP address using its A record.
- When your server sends mail, the receiving server checks the sending IP's PTR (rDNS) record to confirm it matches a legitimate hostname.
A weak link anywhere in that chain — a missing MX record, an unresolvable A record, or absent rDNS — can cause delivery failures or spam-folder placement.
Common issues
- Mail bounces immediately. Usually a missing or misconfigured MX record.
- Mail lands in spam. Often tied to missing rDNS, or missing SPF/DKIM/DMARC records working alongside these.
- Website doesn't load but email works. Check that your A record for the website hostname is correct and separate from your mail server's A record.
FAQ
Can I edit my PTR record myself? Generally no — it's controlled by the owner of the IP address, typically your hosting or network provider, not your domain registrar.
Do I need more than one MX record? It's optional but common, used to provide a backup mail server if your primary one is temporarily unavailable.
How long do DNS changes take to apply? Propagation is often quick, but can take up to a day or two depending on caching by other DNS servers.
