Invalid Emails

What are Invalid Emails?

Invalid emails are addresses that cannot accept delivery at all. They may be syntactically broken, point to a nonexistent domain, or name a mailbox that does not exist on an otherwise valid server. Every send to an invalid address is wasted volume and a drag on sender reputation.

Why it matters

Invalid addresses pile up quickly in any list sourced from forms, imports, or sales leads. Sending to them produces hard bounces, and too many hard bounces signal to mailbox providers that your list is neglected. Marketers, data teams, and anyone importing contacts should validate before sending to avoid burning reputation on messages that had no chance of landing.

How it works

Validation happens in layers. Syntax checks catch obvious typos like missing "@" or "gmial.com". MX checks confirm the domain has mail servers. SMTP probes, or "ping" checks, open a connection and ask the server whether the mailbox exists without actually sending. Each layer catches more, but none are perfect because some servers accept all addresses to hide enumeration.

Examples

• A signup form catching "user@gmial.com" with a typo suggestion
• A lead list of 25,000 where 2,300 addresses fail MX lookup and never get sent
• A validation service flagging role-based addresses like "info@" that often bounce

Best practices

• Validate addresses at the point of capture, before they enter the list
• Run a bulk validation pass on imported legacy lists before first use
• Remove invalid addresses permanently; do not retry them
• Use Sendkit's pre-send validation hooks to catch invalids in real time

FAQs

How is invalid different from a bounce?

Invalid is a category of address that cannot be delivered to. A bounce is the actual event generated when you attempt a send to any undeliverable address, invalid or otherwise.

Can I clean an invalid list instead of deleting it?

Validation services can segment a list into valid, invalid, and risky. Keep only the valid bucket for active sending.

Do catch-all domains return invalid results?

Catch-all domains accept every address at the SMTP level, so probe-based validators cannot tell which mailboxes really exist. Treat those addresses as risky.