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One of the most important steps in any email program whether it be a mass email campaign sending thousands of branded html emails at once or sales automation campaign where you send just a few hundred text-based emails over the course of
a day, is email verification.
If you have too many bad or undeliverable emails in your campaign, you can damage your email reputation
and as a result email service providers (ESP’s) like google, office365, yahoo etc. will either not deliver your email at all or send your email messages to the spam folder.
The quality of your email lists can tell a lot about you as an email marketer. If the ESP’s see you have a high
bounce rate, they will assume you are either sending emails to a purchased list (Non-optin list) or you are not communicating to your contacts very often so your data is bad. So, the ESP’s try to protect their subscribers from unwanted emails by sending any skeptical emails to the spam folder or they might not deliver your email at all.

Email validation is a process that determines if an email address is valid, invalid, role based, malformed or possibly a spam trap.


Email validation is a process that determines if an email address is valid, invalid, role based, malformed or possibly a spam trap.
Some email verification services will also tell you what kind of email domain group belongs to the email address i.e., Google apps, Office365 or General Internet. This information can be very important if you are sending mass email. Why? To send mass email, you need a more control of how your email is sent to control your deliverability.
But before we get into email domain groups let’s get into how emails are created and sent using an SMTP. Sendgrid is a company that provides SMTP Services, and they do a good job of explaining how SMTP’s work here.
In short, SMTP stands for Simple Mail Transfer Protocol, and it’s an application used by mail servers
to send, receive, and/or relay outgoing mail between email senders and receivers.
An SMTP email server will have an address (or addresses) that can be set by the email client or application that you are using and is generally formatted as For example, the SMTP server Gmail uses is, and SendGrid’s is You can
generally find your SMTP email server address in the account or settings section of your email client.
When you send an email, with SMTP host Gmail, AOL, or if your company has their own email server like Microsoft Exchange, the SMTP server processes your email, decides which server to
send the message to, and relays the message to that server. The recipient’s inbox service provider, like Gmail, Yahoo or AOL, then downloads the message and places it in the recipient’s inbox.
Additionally, the SMTP server verifies that the outgoing email is from an active account, acting as the first safeguard in protecting your inbox from illegitimate email. It also will send the email back to the SMTP sender if it can’t be delivered. This informs the sender that they have the wrong email address or that their email is being blocked by the receiving server.

So how does the email verification process work?
Kickbox does a great job of explaining the complexity and technical aspects of verifying an
email address here.
In short, we refer to this process as pinging an email address to see if its valid or not. It’s a technical query where one mail server tries to connect or communicate with another mail server. Through a series of commands or questions determines the validity of that email address.
These mail servers have several codes they send back to each other during this process. SocketLabs does a nice job of listing some of the most important codes here if interested. These codes help the email verification service providers categorize your email addresses. Keep in mind, each email verification service categorizes emails slightly differently.

Email Content

MX Record

Authenticate SPF,



Mail Server

Mail Server Authentication Reputation






At Sales Lead Automation we use EmailOveright for the first verification step and then TowerData
for the second verification step. (We will get into why we use 2 to 3 steps later in this piece).

The most important verification categories include:
Invalid or Undeliverable | Bad emails that have either a syntax error, bad domain or the mailbox doesn’t exist and can’t be delivered.
Spam Traps or Honeypots or Risky | These emails are used to identify and monitor spam email.
Anti-spam organizations, Internet Service Providers (ISPs), and corporations use spam traps to lure spammers. Spam traps can cause your IP address or even your domain to be denied, affecting your sending reputation and email deliverability.
Role Based or Disposable | Emails that might be valid but are addressed to a department i.e., or
Unknown | The mail sever didn’t respond with a code once pinged. So, the only way of knowing if
these emails are any good is to email them and see if they deliver or bounce back.
CatchAll, AcceptAll or Unverifiable | The mail server collects all the email sent to your domain
name not to the actual email address. So, you can send an email to and the
Microsoft mail servers will respond with an acceptall or catchall code. Its not until you send an email
to that you will find out whether that email is any good or not. This is the huge
problem for marketers sending B2B email campaigns because on average 50% of all B2B email data
cannot be verified and is classified as a catchall or acceptall record.
For this reason, Sales Lead Automation uses TowerData as our last step in our email verification process. Tower’s email verification service can verify anywhere from 25-50% of catchall emails. So, let’s say you have 100,000 catchall emails, it is very risky to email these records because the only way to verify these records is to email them. This can cause a high bounce rate and get you blacklisted if not careful. However, if you verify those records using TowerData they have a service that analyzes these catchall records and on average can verify anywhere form 25-50% of these records and
determine if they are good or bad. So, in this scenario if you are trying to verify 100,000 catchall records on average TowerData can verify 25-50k records so in effect you have saved a large portion of your list. Now you can safely add those records to your campaigns and increase your market reach significantly.
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Complainer | The email address belongs to a contact who often complains when someone sends
an unsolicited email. (Note- we like to use these records in our LinkedIn automation programs since they would have to accept our invitation to connect before receiving any email from us).
Malformed | These are emails that aren’t formatted correctly i.e.,
or Shawn@SalesLeadAutomationdotcom are good examples.
Valid | Good deliverable emails that have passed all checks and are safe to email.
Note: all because an email is categorized as valid doesn’t always mean you will reach your contact.
A small percentage of the time a person leaves a company, and that email hasn’t been removed or
forwarded to a new contact yet.

Also note not all email verification providers verify and store the data the same way.
Example, EmailOversight will cache their email verification results for a couple of weeks vs. other email verification providers who might cache their results once every month or 45 days. So, if an email was recently verified as valid 30 days ago, in another verification solution that email might have been verified last week with different results.

Advance Email Verification Strategies
For the reasons mentioned above, Sales Lead Automation will often verify a record several times using
various strategies.
Example: If you are an Apollo user, you will most likely notice you have a higher-than-normal bounce
or undeliverable rate. That’s because they rely on their user community to verify their records. So, if
I email successfully using the Apollo app and that record
gets flagged as valid. Let’s say no one in the Apollo community emails Mark for 6 months there is a very good chance that Mark’s email is no longer any good. Why, perhaps Mark took another job or changed his email 60 days ago to or worse died. That means your email you sent to Mark will bounce or become undeliverable even though Apollo shows Mark’s email is still valid.
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So, let’s walk through the verification process using Mark’s email and our 3 step verification process.

I see that Apollo shows Mark’s email as valid but EmailOversight shows Mark’s email as a catchall
(Unverifiable) but TowerData shows Mark’s email is actually no good or invalid.
As you can see in this example no two email verification solutions are the same or equal. What
might show up as verified in one verification platform might be different in another.
Another reason why email verification platforms might show different results is their partnership
ecosystem. Often these verification providers partner with large scale (Mass email) senders who
share their results of their email campaigns. This deliverability exhaust data will have information on
if the email was valid or not.
Therefore, we prefer to verify our emails in a 2 or 3 step process.
The idea is that if the email can’t be verified with the email verification provider, but that person was
once successfully emailed in Apollo, then the chances are higher that it is still valid email today. Sure,
it’s risky but as I mentioned 50% of all B2B Email Marketing Data can’t be verified. The only way to
know if it’s truly a valid email is to email that person. Well, someone in Apollo has done that for us.
So, if that person is still working at the company on file, chances are high that email will deliver ok.
If you are concerned about your email reputation, then stick with triple verified records like the below image.
We downloaded verified data from Apollo, then verified the record in EmailOversight and then TowerData. All three reported these records as valid.

To further illustrate the point that not all email verification providers are the same, below is an
image of valid records reported by Apollo and TowerData, but EmailOversight shows them as catchall records (Unverifiable). This tells me that EmailOversight partners haven’t emailed this contact record before, and they can’t tell whether it is a good record or not.

And vice versa. Below are records verified in EmailOversight that TowerData shows as Unknown.
Also note Apollo shows this email as Extrapolated meaning this is a guessed email, and that no Apollo user has successfully emailed this person using this email address.

Extrapolated emails are usually generated by looking at other valid email address at the same
domain. So, if the data company has 27 emails from that use first initial, last name @ as their email structure, then they will assume that this person who works at the same company must have the same email structure. (Extrapolated)
Hopefully by now you have learned the ins and outs of email verification along with some advanced strategies to help you clean your lists. All email marketing should begin with some form of email verification to ensure your emails land in the inbox and not the spam folder.