Email validation: what it catches, and what it cannot.
Email validation checks whether an address can exist: syntax, domain, mail server, throwaway providers. It catches typos and obvious junk, but a valid address can still belong to someone else. This guide shows what email validation can do, where it stops and when you need verification instead.
- Four levels of validation
- What no validation can tell
- Validation or verification
Christian Schätzlein, Founder and developer of Sendity
3 min read
What does validation catch?
Tap the addresses a validator rejects, then reveal.
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Valid Correct address, Nina’s own inbox.
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Caught Typo in the domain. A good validator suggests gmail.com.
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Caught Two @ signs: fails the syntax check.
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Caught Throwaway domain, if it is on the provider’s list.
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Valid Role address. Valid, but often read by several people.
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Passes every check Real, existing inbox. Entered by her colleague Max, who wanted the download.
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Confirmed by the message itself The contact comes from the sender of the message, so typos and made-up addresses never reach your list.
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Each level catches more, and none looks into the inbox.
Syntax
One @, a valid domain part, no spaces. This runs in the browser and catches broken input instantly.
Domain and mail server
A DNS lookup shows whether the domain exists and has a mail server (MX record). Typo domains like gmial.com often fail here, and good tools suggest the right one.
Throwaway providers
Lists of throwaway domains catch known services. New domains appear every day, so the lists always lag behind.
Asking the mail server
Some services ask the mail server whether the inbox exists without sending a message. Many servers answer yes to everything or block such requests, so the result is often unclear.
What no validation can tell
Whether the address belongs to the person in front of the form. A colleague’s, a competitor’s or a made-up but existing address passes every level.
Validation or verification?
It depends on what the address is for.
Address typed in a checkout
Validation with a typo suggestion is enough. The customer wants the order confirmation and checks the address.
Sign-up with something to gain
Newsletter, download, giveaway or trial: here people enter other people’s addresses. You need proof that the inbox owner signed up.
Verify without typing
With reverse OTP, the visitor sends one prepared email from their inbox. Nothing is typed, so there is nothing to validate, and the sender is checked by its signature.
Email validation or a sent email?
What you know about an address afterwards.
| Aspect | Email validation | With Sendity |
|---|---|---|
| Typos | Many, with a suggestion | Nothing is typed |
| Throwaway inboxes | Known ones, by list | Most can only receive, not send |
| Someone else’s address | Counts as valid | Only the inbox owner can send |
| Proof | None | Signed email from the inbox |
Where validation still helps.
Validation is not wrong, it answers a smaller question.
Typed addresses
Wherever addresses are still typed, a typo suggestion saves orders and support requests.
Cleaning old lists
Before a mailing, removing dead domains lowers bounces and protects your sender reputation.
Plus verification where it counts
For sign-ups that unlock something, add proof that the owner was there.
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Email validation: common questions.
Does email validation replace double opt-in?
No. Validation shows that an address can exist. Double opt-in shows that its owner agreed. For newsletters you need the second.
Does Sendity block throwaway domains?
Sendity keeps no list of throwaway domains. Most throwaway services can only receive. Where one can send, the email still has to pass the signature check.
Should I block role addresses like info@?
In B2B, info@ is often the real contact. Blocking it costs sign-ups. Accept it, and keep in mind that several people may read it.
How reliable is asking the mail server?
Limited. Large providers and many company servers accept every address at first and only reject later, so the check often answers “unknown”.
Keep reading.
Reviewed for accuracy in by Christian Schätzlein.
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