7 KiB
Below you can find a list of recommended DNS records. While some are mandatory for a mail server (A, MX), others are recommended to build a good reputation score (TXT/SPF) or used for auto-configuration of mail clients (SRV).
References
- A good article covering all relevant topics: "3 DNS Records Every Email Marketer Must Know"
- Another great one, but Zimbra as an example platform: "Best Practices on Email Protection: SPF, DKIM and DMARC"
- An in-depth discussion of SPF, DKIM and DMARC: "How to eliminate spam and protect your name with DMARC"
- A thorough guide on understanding DMARC: "Demystifying DMARC: A guide to preventing email spoofing"
Reverse DNS of your IP address
Make sure that the PTR record of your IP address matches the FQDN of your mailcow host: ${MAILCOW_HOSTNAME} 1. This record is usually set at the provider you leased the IP address (server) from.
The minimal DNS configuration
This example shows you a set of records for one domain managed by mailcow. Each domain that is added to mailcow needs at least this set of records to function correctly.
# Name Type Value
mail IN A 1.2.3.4
autodiscover IN CNAME mail.example.org. (your ${MAILCOW_HOSTNAME})
autoconfig IN CNAME mail.example.org. (your ${MAILCOW_HOSTNAME})
@ IN MX 10 mail.example.org. (your ${MAILCOW_HOSTNAME})
DKIM, SPF and DMARC
In the example DNS zone file snippet below, a simple SPF TXT record is used to only allow THIS server (the MX) to send mail for your domain. Every other server is disallowed but able to ("~all"). Please refer to SPF Project for further reading.
# Name Type Value
@ IN TXT "v=spf1 mx a -all"
It is highly recommended to create a DKIM TXT record in your mailcow UI and set the corresponding TXT record in your DNS records. Please refer to OpenDKIM for further reading.
# Name Type Value
dkim._domainkey IN TXT "v=DKIM1; k=rsa; t=s; s=email; p=..."
The last step in protecting yourself and others is the implementation of a DMARC TXT record, for example by using the DMARC Assistant (check).
# Name Type Value
_dmarc IN TXT "v=DMARC1; p=reject; rua=mailto:mailauth-reports@example.org"
The advanced DNS configuration
SRV records specify the server(s) for a specific protocol on your domain. If you want to explicitly announce a service as not provided, give "." as the target address (instead of "mail.example.org."). Please refer to RFC 2782.
# Name Type Priority Weight Port Value
_autodiscover._tcp IN SRV 0 1 443 mail.example.org. (your ${MAILCOW_HOSTNAME})
_caldavs._tcp IN SRV 0 1 443 mail.example.org. (your ${MAILCOW_HOSTNAME})
_caldavs._tcp IN TXT "path=/SOGo/dav/"
_carddavs._tcp IN SRV 0 1 443 Mail.example.org. (your ${MAILCOW_HOSTNAME})
_carddavs._tcp IN TXT "path=/SOGo/dav/"
_imap._tcp IN SRV 0 1 143 mail.example.org. (your ${MAILCOW_HOSTNAME})
_imaps._tcp IN SRV 0 1 993 mail.example.org. (your ${MAILCOW_HOSTNAME})
_pop3._tcp IN SRV 0 1 110 mail.example.org. (your ${MAILCOW_HOSTNAME})
_pop3s._tcp IN SRV 0 1 995 mail.example.org. (your ${MAILCOW_HOSTNAME})
_sieve._tcp IN SRV 0 1 4190 mail.example.org. (your ${MAILCOW_HOSTNAME})
_smtps._tcp IN SRV 0 1 465 mail.example.org. (your ${MAILCOW_HOSTNAME})
_submission._tcp IN SRV 0 1 587 mail.example.org. (your ${MAILCOW_HOSTNAME})
Testing
Here are some tools you can use to verify your DNS configuration:
- MX Toolbox (DNS, SMTP, RBL)
- port25.com (DKIM, SPF)
- Mail-tester (DKIM, DMARC, SPF)
- DMARC Analyzer (DMARC, SPF)
- MultiRBL.valli.org (DNSBL, RBL, FCrDNS)
Misc
Optional DMARC Statistics
If you are interested in statistics, you can additionally register with some of the many below DMARC statistic services, or self-host your own.
!!! Tip It is worth considering that if you request DMARC statistic reports to your mailcow server, if there are issues with that domain you may not get accurate results. You can consider using an alternative email domain for receiving DMARC reports.
It is worth mentioning, that the following suggestions are not a comprehensive list of all services and tools avaialble, but only a small few of the many choices.
- Postmaster Tool
- parsedmarc (self-hosted)
- Fraudmarc
- Postmark
- Dmarcian
!!! Tip The services may provide you with a TXT record, which you would insert into your DNS records as the provider specifies. This record will give you details about spam-classified mails by your domain. However, please ensure to read the providers documentation from the service you choose, as this process may vary and not all providers may use a TXT record.
Email Test for SPF, DKIM and DMARC:
To test send an email to the email check-auth@verifier.port25.com and wait for a reply. You will get a report back that looks like the following:
==========================================================
Summary of Results
==========================================================
SPF check: pass
"iprev" check: pass
DKIM check: pass
DKIM check: pass
SpamAssassin check: ham
==========================================================
Details:
==========================================================
....
The full report will contain more technical details this is just the first section, we found this to be quite usful for testing both outgoing mail and spam scores.
Fully Qualified Domain Name (FQDN)
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A Fully Qualified Domain Name (FQDN) is the complete (absolute) domain name for a specific computer or host, on the Internet. The FQDN consists of at least three parts divided by a dot: the hostname (myhost), the domain name (mydomain) and the top level domain in short tld (com). In the example of
mx.mailcow.emailthe hostname would bemx, the domain namemailcowand the tldemail. ↩︎