Why you never saw a bounce
A hard bounce is supposed to come back to you with a clear reason. In practice, a lot of mail providers rate-limit, delay, or simply swallow bounce notices to cut down on backscatter spam. The honest state of things: you can send a message to an address that doesn't exist and hear nothing back at all.
So "I never got a bounce" tells you almost nothing. The only way to know for sure is to check the address directly, without sending it anything.
Check it without emailing them again
A verifier asks the receiving mail server whether it would accept a message for that address - no message is actually delivered. In a few seconds you get one of three honest answers:
- The address doesn't exist. Now you know - it's not spam filtering, the address is wrong. Ask them for the correct one.
- The address is real. The problem is somewhere else - keep reading.
- Unknown or Probably valid. Their domain is catch-all or the server won't confirm. The address likely works, but no tool can promise more than that.
If the address checks out, the problem is deliverability
A real, working address can still land in spam, get silently filtered, or sit in a promotions tab the customer never checks. That's not an addressing problem anymore - it's whether your domain is authenticated properly. If you've never checked your domain's SPF, DKIM and DMARC, that's the next thing to look at, not another resend.