How mailbox providers like Gmail judge whether your mail is wanted, based on your sending history: complaints, bounces, authentication and engagement. A poor reputation sends mail to spam.
Example
Meera emails a bought list once, gets many spam complaints and hard bounces, and her next emails to her real customers start landing in spam too. Her domain's reputation took the hit.
How you'll hear it
“Warm up the new domain slowly; we don't have a sender reputation on it yet.”
Don't confuse it with
- Brand reputation: what people think of the business; sender reputation is what mail systems think of your sending.
- Deliverability: the result; reputation is one of its main causes.
Related terms
Sources
- The Marketer's Guide to Email Deliverability, Litmus, 2025
- Email sender guidelines, Google (Gmail Help)