Glossary

What is a secondary sending domain?

A secondary sending domain is a separate domain, close to your company name, that a team uses for cold email so that any reputation damage does not reach the main domain used for customer and staff mail. It needs its own SPF, DKIM and DMARC, a slow start and an honest link back to the real company.

Published by Sellinger AI. Numbers and settings checked on 24 October 2026 against the fact register. Report an error.

Why do teams use one?

Cold email carries more risk of complaints than mail to customers. If the main domain's reputation drops, invoices, support replies and staff mail can start landing in spam too. A separate domain keeps that risk apart. It does not make poor outreach acceptable; it limits the damage of mistakes.

How do you set one up?

Choose a name that clearly belongs to your company, such as a short variation of it. Avoid names that look like another brand.
Set up SPF, DKIM and DMARC exactly as on the main domain.
Point the website of the secondary domain to your real site, so people who check it find you.
Create real mailboxes for real people, with signatures and the company address.
Start slowly, with low daily volume and a warm up.

What should you not do?

Do not use a secondary domain to hide who you are. Several laws require you to identify yourself in commercial email, and the US CAN-SPAM Act bans misleading header information. The domain is a technical separation, not a disguise. See CAN-SPAM Act.

How Sellinger handles it

You can connect any Gmail or Outlook mailbox to Sellinger, including mailboxes on a secondary domain. Every connected account has daily limits that the agent cannot exceed, set per account. LinkedIn defaults are 20 invitations a day and 150 a week. Email defaults to 50 sends a day per mailbox, with an optional warm up that starts at 5 a day and doubles every 3 days up to the limit.

Sellinger sends from your own connected Gmail or Outlook mailbox. It does not set up or check your domain records, run inbox placement tests or monitor your domain, so you or your IT provider set up SPF, DKIM and DMARC at the domain. Before every send on email, LinkedIn and WhatsApp, the platform checks the team's suppression list and refuses the send when the contact is on it or when the check cannot be completed, across every connected mailbox in the team.

Common questions

Is a secondary domain spam?

No, if it clearly belongs to your company and you follow the same rules. Using one to hide your identity is the problem.

How many mailboxes per domain?

There is no fixed rule. Fewer, well used mailboxes are easier to keep healthy than many idle ones.

Does the suppression list cover all domains?

In Sellinger it is a team list, checked before every send on any connected mailbox.

Sources and method

General deliverability practice; CAN-SPAM requirements from the FTC compliance guide as summarised in is cold email legal. Sellinger behaviour from the fact register, checked 24 October 2026.