Email Verification Best Practices

The Warmup Inbox Team
The Warmup Inbox Team

Why Is Email Verification Important?

First and foremost, email verification helps improve email deliverability. If you send emails to inactive addresses, it can damage your reputation or get your domain placed on a blocklist. Taking a moment to verify emails before adding them to your subscriber list increases the likelihood that your emails won’t bounce and decreases your chances of falling into a spam trap.

Email campaigns can be extremely effective when the messages reach the intended inboxes, but collecting emails from customers can be set back by simple human errors. Whether they type their address in wrong by switching or dropping a letter or using the wrong domain, you can have an email added to your subscriber list that leads nowhere. Or, if you have a person manually entering email addresses to your contact list, they may misread a specific letter or number or confuse an underscore for a dash, and again you have a bunch of emails that lead to dead ends.

Verifying emails before you hit send increases email deliverability, audience reach, and the success of email campaigns. At the same time, it decreases the number of hard bounces, spam reports, and blocks you receive. While checking each new email as you add it to your list can seem tedious, it can significantly boost your sender reputation.

Verifying your email can be done in three easy steps:

  1. Syntax and Formatting ChecK
  2. Server Confirmation
  3. Mailbox Validation

Syntax and Formatting Check

The first thing a verification service will analyze is an email’s syntax, or the basic construction of the email address. Multiple email providers have specific specifications regarding the email addresses people can register. For example, Yahoo doesn’t allow addresses to begin with a number. So, if an email starts with a number and ends with “,” it’s fake. Verification services will check addresses against the server’s protocol for email syntax.

After reviewing the address’ syntax, the service will check the email formatting. The formatting consists of regulations that dictate what can be used for an email address. Because thousands of permutations have to be analyzed, there’s no way to check formatting manually without wasting a lot of time. Thankfully, there are tools you can use to rapidly check all of these permutations, from ensuring the “@” sign has been used to identifying any special characters that aren’t allowed in an email address.

Server Confirmation

Once the syntax and format have been analyzed and verified, the verification service proceeds to server confirmation. The service checks the DNS records for the domain name of the email address. The domain name is what comes after the “@” symbol. The service tests the mail exchanger to make sure that the email address can accept emails.

Incoming emails will bounce if the inbox is full, so the domain or server confirmation will identify addresses that are authentic but unable to accept new mail. Your marketing team can’t determine whether a recipient’s inbox is full before sending an email to them, and any kind of email bounce can damage your reputation. Using a service to check this can help keep your delivery rate high and your reputation in good standing.

Mailbox Validation

The last step involves the service validating the mailbox. The service will attempt to contact the SMTP server to see whether the address exists. If the server responds positively, the address is ready to accept emails.

The verification service pings the email address with an EHLP message and then waits for the email server to respond. When the server responds, it confirms that the email exists on the server and is active.

An excellent email verification service is able to check emails without sending a message because of the automatic process it employs. When automated, the process can take a small amount of time and yield phenomenal results. You can also use email verification services to check for duplicate emails, role accounts, and spam traps.

In addition to the three steps we mentioned, you can strengthen your email list from the beginning by using double opt-in measures that allow the customer to verify their email address before being placed on the mailing list. But if you’re sending cold emails, using a verification service is a fantastic way to ensure a clean mailing list.

VRFY Command

Another way to verify addresses is with the VRFY SMTP command. The VRFY command is used to confirm whether a mailbox exists on the local host. For example, if you wanted to check if “example” had a mailbox through the host “,” you could run the command

>>-VRFY--example-------------------------------- ><

And if the address is valid, the query would return something like:

SMTP client: VRFY example

SMTP server: 250

The VRFY command works the same as the Expand (EXPN) command and can verify the existence of one or more mailboxes within the system. Configuration statements within the SMTP.SMTP.CONFIG dataset defines the mailboxes. The MVS SMTP server verifies only TSO user IDs if RACF is installed on the local system. TSO user IDs that are verified as valid are registered with a reply code of 250. If RACF is not installed, any character string of eight characters or more is assigned the reply code of 250.

However, the issue with the VRFY command is that it’s not entirely practical since many servers don’t allow remote connections to verify addresses.

Broken SMTP Handshake

One last option is to use a broken SMTP handshake. In a typical SMTP conversation, the final command would be “DATA,” alerting the server that the client is ready to send the message content. Once the content is sent to the server, if the server accepts the message, the client can either send another message or use the “QUIT” command to close the connection.

However, you go through the SMTP conversation but don’t send the data with a broken SMTP handshake. This allows the server to accept or reject the recipient’s email address without sending a message, and all you have to do is reset, quit, or close the TCP connection.

The issue with a broken SMTP handshake is that running this verification test thousands of times can result in your IP being placed on a blocklist. Another problem is that you may get the wrong response through this check because of the applications a server uses. Specific anti-spam gateways don’t run a recipient check until the message is received so that you may get a false green light. Or, if a server uses a gray list, the verification may show that the email address is inactive when it’s actually active.

Email Verification