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How to Add a Second Sending Domain in BillionMail (DNS, SSL and Mailboxes)

One BillionMail server can send and receive mail for many domains: your main brand, a second website, a client, or a separate newsletter subdomain like

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news.example.com

. Each domain gets its own DKIM key, mailboxes and settings. This guide adds a second one.

Domain or subdomain?
A common setup is to send newsletters from a subdomain (for example

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news.example.com

) and keep the main domain for normal mail and password resets. Mailbox providers track reputation per domain as well as per IP, so a newsletter problem then doesn't drag down your important mail. Either way, the steps are the same.

Step 1: Add the domain
Open Domain and click Add Domain. This is the form:

• Domain: the new domain, without
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  www
  or
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  https://
  , for example
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  example.net
  .
  
• Domain Quota and Mailbox Count: the total storage and the number of mailboxes this domain may use.
  
• Dedicated IP: only if your server has more than one public IP and you want this domain to send from its own. Test Connection checks the IP works. Leave empty otherwise.
  
• Hostname: the mail hostname for that IP, if you set one. Its reverse DNS must match.
  
• Catch All: forward mail sent to non-existent addresses to one mailbox. Handy for a small business, but it also catches a lot of spam.
  

Click Confirm. The domain appears in the list with its quota, mailboxes, SSL status and actions.

Step 2: Publish the DNS records
Click DNS Records next to the new domain. BillionMail shows the records to add at your DNS provider: MX, SPF, DKIM and DMARC (plus an A record for the mail host if you use a new one). Each domain has its own DKIM key, so copy them from this domain's page, not the first domain's.

A few tips:

• If you use Cloudflare, set mail-related A records to DNS only (grey cloud). Mail can't go through Cloudflare's proxy.
  
• The MX can point to the same mail hostname as your first domain, for example
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  mail.example.com
  . You don't need a new hostname for each domain.
  
• Only one SPF record per domain.
  

Wait for the records to turn green. Details for each record are in BillionMail DNS setup explained; if DKIM stays red, see DKIM fails even though the record exists.

Step 3: SSL
The SSL column shows the certificate status and days left. BillionMail requests a Let's Encrypt certificate once DNS points to the server. If it fails, see SSL certificate won't apply.

Step 4: Create mailboxes
Under Mailboxes, add the addresses the new domain needs. At minimum:

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postmaster@

and

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abuse@

, plus the sending address such as

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[email protected]

. See mailboxes and webmail.

Step 5: Choose which domain sends

• Set Default in the domain list makes a domain the default choice in forms.
  
• For each campaign, pick the domain and mailbox in the From field.
  
• For the Send API, the domain is part of each API's settings. See the Send API guide.
  
• If you use a relay, bind it to the domain under SMTP. See SMTP relay setup.
  

Step 6: Test and warm up
Send a test from the new domain to Gmail and check Show original for SPF, DKIM and DMARC PASS. A new domain has no reputation yet, even on a warm IP, so grow its volume slowly. See the IP warm-up plan.

Removing a domain later
Delete in the domain list removes the domain. Before you click it, export or move any mail you want to keep from its mailboxes. Remove its DNS records afterwards.

More BillionMail guides

• Send API for transactional email
  
• WordPress email through BillionMail SMTP
  
• Import contacts, groups and tags
  
• Email templates explained
  
• SMTP relay with Amazon SES, Brevo or Mailgun
  
• Mailboxes and webmail
  
• Campaign analytics explained
  
• IP warm-up plan
  
• Move from Mailchimp or Sendy
  
• Send your first newsletter · DNS setup explained · Deliverability testing
  

Applies to BillionMail 4.9, October 2026. Replace

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example.com

and

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mail.example.com

with your own domain and mail hostname. Menu names can change a little between versions.