A store gets a run of new accounts with addresses like random letters at domains that don't exist. Nobody notices until the welcome email goes out and every one of them hard-bounces. On a sending domain that's still warming up, a cluster of hard bounces is exactly the signal mailbox providers watch for.
Sometimes it's a bot probing the signup form. Sometimes it's someone's own test run with made-up addresses. Either way the addresses are fake and your domain pays for them.
Stop them at the form
- A CAPTCHA or Cloudflare Turnstile on account registration and newsletter forms.
- A hidden honeypot field that real people never fill in.
- A limit on how many accounts one connection can create in a short time.
- Address checks on the form that catch typos like gmial.com.
Stop them before the send
Some will get through anyway. TellySend checks every address before it sends: if the address's domain has no mail server at all, the address is suppressed and never mailed. That catches made-up domains. It can't catch a made-up mailbox at a real domain, like a random name at gmail.com. That's what double opt-in or a verification service on the form is for.
Watch the bounces
A healthy list rarely hard-bounces. If one send's bounces jump, look at where those contacts came from before you send again. TellySend pauses an account's sending automatically when bounces or complaints spike, so one bad batch can't keep hitting the domain.