Every email list decays. People change jobs, abandon inboxes and mistype addresses in signup forms. Industry estimates put list decay at roughly 20-30% per year, which means a list you collected last year is already full of addresses that will bounce.
High bounce rates hurt more than a single campaign. Mailbox providers like Gmail and Outlook watch your bounce and spam-trap rates, and a poor score pushes even your good emails into spam folders.
What a good verification check looks at:
- Syntax and domain checks (is the address formatted correctly, does the domain have MX records?)
- Mailbox existence via an SMTP handshake, without actually sending a message
- Disposable / temporary addresses that are only used to grab a freebie
- Catch-all domains that accept everything, so you know which results are risky
- Role-based addresses such as info@ or sales@, which often have low engagement
Two ways to use it:
1. Clean an existing list in bulk before a campaign: email list cleaning
2. Validate addresses in real time at the point of signup with an email verification API
Real-time validation is the better long-term habit, because bad data never enters your database in the first place.
Disclosure: I work on SendBridge, a Czech email verification service. It has a free plan with 100 checks per month if you want to test your own list.