To route mail to OpenSRS hosted email, you point your domain's DNS records at the OpenSRS mail servers. This article explains the record types involved and gives example configurations for both hosted email and filter-only setups, in the Test and Live environments.
About DNS for hosted email
DNS (Domain Name System) maintains many record types, but two matter for the OpenSRS Email Service: MX records and CNAME records. The MX record directs incoming mail to the right server, and the CNAME record lets your clients reach OpenSRS POP, IMAP, and SMTP servers through a friendly hostname on your own domain.
Warning: Do not make any DNS changes until the domain and mailboxes are set up on the OpenSRS Email Service. Pointing DNS at the servers before the accounts exist disrupts mail delivery.
Mail Exchange (MX) records
The MX (Mail Exchange) record is the line in a domain's DNS zone file that directs email for that domain to the correct mail server. It tells the rest of the internet where the mailboxes live.
A zone file is the file on a name server that holds a domain's DNS records, including the data needed to resolve the domain name to IP addresses. When a domain uses more than one mail server, you can list multiple MX records and assign each a preference number that sets the order in which servers are tried. This supports primary and backup mail servers.
Canonical Name (CNAME) records
A CNAME (Canonical Name) record maps one hostname to another, so several hostnames can resolve to the same destination. OpenSRS uses CNAME records to identify the OpenSRS POP, IMAP, and SMTP server, which lets your users connect to a friendly hostname such as mail.yourdomain.com instead of the underlying yourdomain.com.cust.<cluster>.hostedemail.com address.
Warning: Do not use A records or IP addresses in place of CNAME hostnames. If you point to a fixed IP and OpenSRS later changes that IP, mail service breaks. CNAME records keep working through IP changes.
About clusters in DNS records
OpenSRS Email runs on two clusters, A and B, shown as <cluster> in the examples below. Cluster B adds a .b component to the hostname; Cluster A adds nothing. If you omit the cluster from a record, the system defaults to Cluster A.
Note: If you do not know which cluster you are on, see Which Email Cluster Am I On?
Example DNS configurations for hosted email
In every example, replace example.org with your own domain.
Test environment (hosted email)
There is one Test environment. Use this configuration for a domain in Test.
mail.example.org. IN CNAME mail.example.org.cust.test.hostedemail.com.
example.org. IN MX 0 mx.example.org.cust.test.hostedemail.com.
Live environment (hosted email)
For email accounts on a root domain, such as admin@example.org, use records of this form (replace <cluster> with your cluster, or leave it out for Cluster A):
mail.example.org. IN CNAME mail.example.org.cust.<cluster>.hostedemail.com.
example.org. IN MX 0 mx.example.org.cust.<cluster>.hostedemail.com.
For email accounts on a subdomain, such as admin@finance.example.org, use:
finance.example.org. IN CNAME mail.example.org.cust.<cluster>.hostedemail.com.
finance.example.org. IN MX 0 mx.example.org.cust.<cluster>.hostedemail.com.
Example DNS configurations for filter-only service
The filter-only service uses a CNAME for the web-based spam quarantine and an MX record for incoming mail. The prefixes spam, portal, and spamportal are all acceptable for the quarantine hostname.
Test environment (filter-only)
spam.example.org. IN CNAME mail.example.org.cust.test.hostedemail.com.
example.org. IN MX 0 mx.example.org.cust.test.hostedemail.com.
In this example, the web-based spam quarantine is at http://spam.example.org/, the IMAP server is spam.example.org, and the mail exchange is at example.org.
Live environment (filter-only)
portal.example.org. IN CNAME mail.example.org.cust.<cluster>.hostedemail.com.
example.org. IN MX 0 mx.example.org.cust.<cluster>.hostedemail.com.
In this example, the web-based spam quarantine is at http://portal.example.org/, the IMAP server is portal.example.org, and the mail exchange is at example.org.
Allowlisting the OpenSRS Email Service
To make sure filtered mail reaches your users, add the IP ranges that OpenSRS sends filtered mail from to your allowlist.
Environment | IP ranges |
|---|---|
Cluster A | 216.40.44.0/24, 216.40.42.17/32 |
Cluster B | 64.98.42.0/24, 64.98.36.17 |
Test | 216.40.41.5/32, 216.40.41.17/32 |
Tip: Confirm these IP ranges with OpenSRS Support before you rely on them for troubleshooting, as filtering IPs can change over time.
Next steps
- Identify your cluster. Find the correct hostnames for your records. See Which Email Cluster Am I On?
- Set up the filter-only service. If you are filtering mail for an existing server, follow Setting Up the Email Filter-Only Service.
- Add domain aliases. Remember each alias needs its own DNS records. See Adding and Removing Domain Aliases.
Questions? Contact OpenSRS Support.
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