# DNS, PTR, and Reverse DNS > DNS records identify your domain, while reverse DNS helps inboxes check whether a sending IP has a sensible hostname. - Human page: https://mailrith.com/guides/dns-and-reverse-dns - Markdown page: https://mailrith.com/guides/dns-and-reverse-dns.md - Category: Authentication and Deliverability - Reading time: 7 min read - Related keywords: DNS PTR and Reverse DNS, DNS PTR and Reverse DNS guide, Authentication and Deliverability, Authentication and Deliverability guide, email sending guide, email marketing guide, email deliverability guide, SPF, DKIM, DMARC ## AI Agent Notes - Use this page as plain-language guidance for the specific email sending issue named in the title. - Preserve the distinction between Mailrith, an email delivery service, DNS, and inbox providers when explaining fixes. - When a user is running a free tool, pair the tool result with the relevant issue or step section from this guide. ### DNS, PTR, and Reverse DNS DNS records identify your domain, while reverse DNS helps inboxes check whether a sending IP has a sensible hostname. DNS is the public record system for domains. It tells the internet where to find services and how to verify domain-related settings. Email authentication depends heavily on DNS. [SPF](https://mailrith.com/guides/spf.md), [DKIM](https://mailrith.com/guides/dkim.md), [DMARC](https://mailrith.com/guides/dmarc.md), tracking domains, bounce domains, and sometimes BIMI all use DNS records. If DNS is wrong, inboxes may not be able to verify the sender even when your email delivery service dashboard looks mostly configured. The three DNS details you check most often are record type, host name, and value. The type might be TXT or CNAME. The host name might be `selector1._domainkey` or `_dmarc`. The value is the long text or target from your email delivery service. A common mistake is adding the right value at the wrong host name. For example, an email delivery service may ask for a record at `selector1._domainkey.example.com`, but the DNS dashboard may expect only `selector1._domainkey` because it already appends `example.com`. Read the DNS UI carefully. Another common mistake is creating duplicate records. SPF usually needs one TXT record at a host name. Adding a second SPF TXT record beside the first one can break SPF. DKIM is different because each selector usually has its own record. Reverse DNS, also called PTR, works from the sending IP address back to a hostname. Some inbox providers expect the sending IP to have a PTR record, and for that hostname to point back to the same IP. This is usually managed by your email delivery service, not by Mailrith. If you use a major email delivery service, that service usually manages the sending IP and reverse DNS. Your job is usually to add that service's domain DNS records correctly. If you manage your own SMTP server, you must pay closer attention to forward DNS, reverse DNS, TLS, and IP reputation. 1. Open the exact DNS zone for the sender domain or subdomain. 2. For each record from your email delivery service, identify the record type, host name, and value. 3. Add the record exactly as your email delivery service expects, accounting for whether your DNS host appends the domain automatically. 4. For SPF, check whether a TXT record already exists at that host name and merge service instructions when needed. 5. For DKIM, add each selector record your email delivery service gives you. 6. For DMARC, add or update the TXT record at the `_dmarc` host for the From domain. 7. Wait for DNS propagation and use your email delivery service's verify button. 8. Send a test email and inspect SPF, DKIM, and DMARC results. 9. If you run your own SMTP server, confirm PTR reverse DNS with your hosting provider, not only inside your DNS dashboard. - Copy the DNS records from your email delivery service exactly, including host names and values. - Wait for DNS propagation before assuming a new record is live everywhere. - Avoid editing SPF, DKIM, or DMARC records casually during a live campaign. - SPF records usually live as TXT records and should not be duplicated at the same host. - DKIM records usually live under `_domainkey` and are often separated by selector. - DMARC records live under `_dmarc` for the domain in the visible From address. - If you run your own SMTP server, confirm forward DNS and reverse DNS are set correctly. - Keep a list of which email delivery service or system owns each sending domain, subdomain, and DNS record. - If authentication suddenly fails after a DNS change, compare the current DNS records with the expected records from your email delivery service. - Read [SPF](https://mailrith.com/guides/spf.md), [DKIM](https://mailrith.com/guides/dkim.md), and [DMARC](https://mailrith.com/guides/dmarc.md) before deleting records you do not recognize. ## Fix Common Issues ### DNS Lookup Failed A checker could not complete a public DNS lookup. This can happen because the domain is invalid, DNS is temporarily unavailable, or a recent change has not propagated yet. 1. Check that the domain is spelled correctly and does not include a URL path. 2. Open the DNS provider for the domain and confirm the record exists there. 3. If you recently changed DNS, wait for propagation and try again. 4. Check your email delivery service's verify button because it may use a different resolver. 5. If DNS keeps failing for several tools, confirm the domain's nameservers are correct. ### No Mail-Server IPs Found A checker found MX hosts or a domain, but could not find IPv4 addresses to check for mail-server reputation. 1. Confirm the domain has MX records if it should receive mail. 2. Open each MX host in your DNS provider or mailbox provider dashboard and confirm it resolves to an IP address. 3. If an email delivery service manages the mail servers, ask that service which sending IPs or pools should be checked. 4. If you entered a domain that is only used for links or tracking, check the actual sending domain or sending IP instead. 5. Run the blacklist checker again with a specific IPv4 address if your email delivery service gives one. ### PTR Record Missing A PTR or reverse DNS checker found an IP address that does not return a hostname. 1. Confirm the IP address is really used for sending mail. 2. Find out who owns the IP address. This is usually your email delivery service, hosting provider, cloud provider, or internet service provider. 3. Ask that provider to set reverse DNS for the IP. You usually cannot add PTR records in your normal domain DNS dashboard. 4. Use a hostname that belongs to a domain you control or that your email delivery service manages for sending. 5. After the provider updates reverse DNS, run the PTR checker again. ### PTR Does Not Point Back to the IP A checker found a PTR hostname, but that hostname does not resolve back to the same sending IP address. 1. Copy the PTR hostname shown by the checker. 2. Check the A record for that hostname. 3. Ask the IP owner or hosting provider to make the PTR hostname and A record match the sending IP. 4. If your email delivery service manages the IP, send them the checker result and ask them to correct the mail-server identity. 5. Run the PTR checker again after the DNS change has propagated. > When email delivery service verification fails, check the host name first. Many DNS mistakes happen because the DNS dashboard silently adds the main domain to the host name. Related resources: - [SPF](https://mailrith.com/guides/spf.md): Understand SPF TXT records and duplicate-record mistakes. - [DKIM](https://mailrith.com/guides/dkim.md): Understand DKIM selectors and DNS keys. - [DMARC](https://mailrith.com/guides/dmarc.md): Understand where the DMARC record lives and what it does. ## Related Guides - [Sender Domains and Email Authentication](https://mailrith.com/guides/sender-domains-and-authentication.md): Your sender domain is the name inboxes learn to trust, and authentication proves that your email delivery service is allowed to send for it. - [From, Reply-To, and Return-Path](https://mailrith.com/guides/from-reply-to-and-return-path.md): An email has several sender-related addresses, and each one has a different job in delivery and replies. - [Email Headers and Message Format](https://mailrith.com/guides/email-headers-and-message-format.md): Message headers, MIME structure, and basic formatting rules help inboxes parse and trust an email.