Frequently asked questions

What is an email bounce?

An email bounce is an automated message from an mail server that informs the sender that their email has not been delivered to its intended destination. This will indicate that something has gone wrong either on the sender side or the recipients’ side.

Is it safe to use a free email bounce checker?

The tool offers 100% privacy as at no point the entered data is logged or stored to our servers.

How many emails can I verify at a time?

As of now the tool sets a limit of 10 emails for a single go.

What are the types of email bounce status returned?

The tool returns three type of statuses :
  1. No bounce : Means that the email addresses are valid.
  2. Soft bounce : Means that the email addresses are temporarily unavailable. The tool returns this error for all kinds of errors from typos, patterns, SMTP validation failing due to unknown causes or mail server unavailability, etc.
  3. Hard bounce : Means that the email addresses are permanently unavailable. The tool throws this error when no MX records of the given addresses are found.

What is SMTP validation and what are the email providers supported?

The tool performs SMTP validation when the SMTP checkbox is checked and vice versa. The SMTP validation involves establishing a socket connection with the mail server and simulating the sending of an email. This being the most trickiest part of the entire validation process can return false negatives cause of certain settings at the mail server end(Most mail servers have some sort of checks to block spam). The tool has returned successful SMTP validation checks for the following domain names :,, If your list to be checked includes other domain names there is a high chance of getting false negative results (Soft bounce warning mostly) for even valid email addresses if the SMTP flag is set.

Is BlockSurvey email bounce checker open source?

Yes, the tool is open source and the links to the source code can be found in the app page.

Is this email bounce checker a honey pot?

Here at BlockSurvey, we give at most importance to privacy which is consistent with our vision of a world having a decentralized internet space. As already mentioned above, the tool does not collect and store any form of data given to it. It simply acts as a platform for people to enter their emails and get them validated.

Why is it free?

The product is built from already existing open source code with slight tweaks by us. It was primarily built for weeding out burner and disposal emails from our own product i.e. BlockSurvey and at a certain point we had this idea of sharing the benefits accruing from this project with the rest of the world.

What are the modules used to build this?

The tool uses a npm module called "deep-email-validator". link :

How does email bounce checker work?

The tool checks for Regex, Typos error as a first step and then goes to check if the email address is present within the list of disposable email domains, then comes the check for the MX record followed by the SMTP check(if the flag is set). The tool returns a status of 'No bounce' if all the checks return true and in case of error based on the error type we return the status of either 'Soft bounce' or 'Hard bounce'.