How Much Time Email Validation Takes?

It has been several years since we are performing email validations in bulk, single, and API methods (for some users). Most of the customers ask us questions about the validation speed and how much time it takes to validate for example 10K or 100K email addresses.

The answer to this question is not as simple as a number – for example 15 minutes. I am going to describe it in this blog post. First of all, we need to know what is your validation method. Are you going to use bulk email validation or validate single emails using the API? What is the turnaround time of an email validation engine to validate an email list?



What is the Difference Between Bulk Email Validation and the API?

The short answer is anti-greylisting technology. Anti-greylisting in the validation process is the technology of purposeful pauses between multiple validations. It tries to simulate the behavior of a well-configured email server to prevent IP blocking. Technically, an API is built to send validation results as fast as it can. So, if anti-greylisting is enabled on the API, it could take 15~45 minutes for each API call – which is unacceptable. This is why anti-greylisting can be enabled only on bulk email validations. The main point of anti-greylisting is to overcome the number of “Unknown” results. So, if you validate the same list using the bulk engine and the API, you must expect a higher amount of “Unknowns” on the API results.

Anti-greylisting Technology

Anti-greylisting is built to simulate a well-configured email server and reduce the number of “Unknowns”. The receiving mail server tells the sender, to please retry to send the email again in (X) minutes. A well-configured mail server will attempt to resend an email at different intervals until it’s accepted or rejected by the receiving mail server. Each mail server has a different time they greylist the sender for, per email, normally between 1 and 30 minutes. Clearalist deploys breakthrough anti-grey-listing technology. When it encounters any greylisting, it will wait 15 minutes and retry to validate those specific emails. This reduces the amount of “Unknowns” received back. So you wait a little longer for your results when validating them, but your results will be a lot better. It doesn’t matter how many greylisted email addresses you upload, whether it’s 1 or 100,000. The processing is only delayed by 5-15 minutes in total if you use it as a service for email validation. Email validation takes more time using anti-greylisting, but it’s worth it.

Validation Time-out

Some email servers have a high time-out. It could take up to 45 seconds to receive a response from them. Contrary to the API, the bulk validation engine has a timeout of 45 seconds.

Considering anti-greylisting technology and the validation timeout in mind, it is hard to predict the validation processing time of a certain list. 10K Gmail addresses do not need anti-greylisting and the validation takes only 1 second for each email. It means the Clearalist engines validate 10K emails in only 70 seconds. On the other hand, 10K emails with a response time of 45 seconds + anti-greylisting technology need around 60 minutes to validate.



Email validation requires time. API needs to respond as fast it can. But bulk email validation needs time to process email lists. It is a bad idea to remove anti-greylisting technology and reduce the validation time-out to increase process time. Of course, the results will be ready in less time, but it contains numerous unknown validation results. Email validation is not a job that must be done in a hurry. Let the process finish on its own terms.


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Email Validation Process: How Email Verification Really Works