A client has provided us with an excel spreadsheet of around 10,000 email addresses, names and addresses. They were taken from a CRM used previously.

I've been asked to "clean" up this database - such as check for invalid addresses - (email format, existing mailboxes etc).

I've done a bit of Googling and came up with a few "Email List Cleaning Services". Here is one such company.

Now my question is - does anyone have any experience with this kind of service, and is it a legitimate service?

Alternatively, what are my options for "cleaning" this list?

I ask as MailChimp, our preferred email marketing tool, will terminate account access if a certain percentage of emails bounce, (and I imagine similar e-shot services operate on the same basis), to comply with anti-spam regulations etc.

This is a legitimate cause, although it may sound quite the contrary.

4 Answers 4


I would imagine you could do this legitimately by connecting to each addresses SMTP server and starting an SMTP session, going as far as giving the address the message was for but resetting and quitting the session before sending an data. assuming the responses until that point had been 250 OK you could assume the address was valid.

the wikipedia SMTP page gives an example of an SMTP session, the test session would be the same up to the DATA command where you would send RSET then QUIT instead of feeding in an actual email.

The problem would be that SPAM blacklists use "honeypot" addresses that an only be acquired by scraping websites. They assume that should you send one of those addresses a message you must be a spammer and may ad you to their blacklist. The above test would not filter these addresses there is no way you could.

UPDATE I looked at the link you gave after I wrote the above. I wasn't expecting them to give such a detailed account of their process. Step 5 will be as I have detailed above. The other steps seemed sensible. The pricing seemed fair.

  • The way to avoid honeypot addresses or other blacklist risks is to not be a spammer. If you're abiding by the law and using opt-in lists only, then you're not likely to encounter such addresses. If you want to guarantee that such addresses aren't intentionally submitted by a competitor trying to sabotage your company, then use a double opt-in list, which is best practice anyway. Mar 23, 2012 at 15:57
  • Also, the real limitation of such list cleaning services is that some SMTP servers are not publicly accessible like that (in order to prevent abuse by spammers), and certain exchange servers won't reveal non-existent addresses as a way to also not reveal existent addresses to spammers. So that's the real problem. But otherwise your answer is spot on. Mar 23, 2012 at 16:02

The best you can hope to do without actually sending out emails to each address, is to check the email syntax.

At the most basic level, check for an @ sign and a . character, if you wish to get more advanced, there are several regular expressions which will help validate the syntax of an email address.

The important point to make is that you can ONLY check the syntax, that doesn't mean its a real email address with a real person on the other end.


Mailing list cleaning/data scrubbing is a legitimate practice in both email and offline marketing. In fact, it's the most crucial component to list hygiene. This is also partly why some companies prefer to use leased lists (though this can be considered spammy, especially if you aren't careful about the source), as such lists are professionally managed and kept clean of duplicates and dead/outdated addresses.

A professional list cleaning service should be able to help you merge/purge and split your mailing lists and scrub invalid addresses. But you should also make sure you're removing bounced addresses as they come in and using e-mail analytics to check your lists for inactive addresses. Using a double opt-in list and maintaining clear unsubscribe instructions in each e-mail (and an automated unsubscribe system) is the other half of the puzzle. This way your lists will keep themselves clean and you won't need professional list cleaning services as often.


Email list "cleaning" is a very good practice that helps you to improve your email delivery rates and sender reputation. We highly recommend our customers to use 3rd party software to check their lists and to remove any invalid mail addresses prior to any mailouts. While you can try to clean your mailing list manually by deleting invalid format email addresses, previously bounced email addresses etc., professional services do this job better. Email List Cleaning is a service we recommend that some of our customers have used and said was very effective.

Relative to the service you mentioned, I'm not familiar with it, but you can try how it works and tell us the results.