Frequently Asked Questions

How does e-mail work?

When an e-mail is sent, the following actions are taken:

How does work? looks up the SMTP server responsible for the e-mail address, and tries to establish an SMTP connection. It then tries to send several commands, almost as if an e-mail is going to be sent. When enough information is gathered, the connection is aborted. No actual e-mail is sent.

Does always work?

No, not always. Verifying e-mail is not possible a 100% of the time.
The valid syntax of the address and the domain (= the part after the @-sign) can always be verified.
However, the local part (= the part before the @-sign) may not be possible in some cases. A few examples:

Any mail verification service will run into these same challenges. Other solutions may flag the mail as valid, but will show the real status.

Is e-mail guaranteed to either be delivered or bounced?

No. There is no guarantee an e-mail is delivered, even if you didn't receive a bounce-mail.
There are several possible scenarios where you would not receive a bounce mail.
For example: when an SMTP server suddenly finds itself isolated from the Internet, it will not be able to send a bounce-mail.
Or maybe your address is not reachable so the bounce mail could not be delivered to you.

Is it possible that I can send e-mail, but not receive anything (or the other way around)?

Yes, sending and receiving are completely different things.
For sending you need to be able to contact the SMTP server.
For receiving you need to have access to your mailbox, usually via POP3 or IMAP. For mail to be able to arrive into your mailbox, your mailserver has to be registered in the DNS system, and it has to be reachable from the Internet.
Since sending and receiving are completely different actions, one can sometimes work while the other doesn't.

Where does come from?

A lot of people come to me asking if a certain e-mail address is having problems or why a certain e-mail address doesn't work. Usually the answer is in the bounce-mail, but often it is in such technical terms most people don't know what it means.
There are some routine tests I usually do to find out more about an e-mail address.
I decided to automate these tests, and make them available for everybody on this site.

Can I get the source code?

No, the source of is not available.
If you are looking for open source maybe these projects (from the same author as may be interesting:

Is free?

Yes, is free for individual e-mail address when checked via the website.
The site displays advertising as a way to make revenue.

Can check a whole database for me? has developed a program that can do this. Please go to the download page for more information.

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