Email list verification is one of the most challenging parts of email list hygiene. Everyone want their email list cleaning free, but in this case, you really get what you pay for. Out of the dozens of competitors in this field, all of them know that it’s not easy to verify if an email is a catch-all, soft bounce or hard, and on top of that, report back the exact details of the “kind” of bounce it really is. In order to verify an email, several things need to occur. There are approximately 30,000 internet service providers worldwide and each one sets their own mail parameters using blacklists to monitor and block spam. Each one is unique, therefore the approach must be handled delicately in order to not be blocked, blacklisted or worse, have false positives sent back during the exchange.

Some servers will tell us that the delivery has failed, but no information was given if the email exists. Simply labeled an “Error”, these could be network communication errors where power went out during or before the exchange. Errors also happen when the recipient server is upgrading. An “SMTP Error” is an SMTP answer from the recipient server that the email is invalid or reported as an internal error to us. Since we send SMTP handshakes for verification, this exchange happens when the connection is interrupted due to improper setup on their end, connection disconnected during the exchange or security protocol interruption.

An “SMTP Protocol” happens when the destination server allowed us to connect but the SMTP session was closed before the email was verified. The reason it closed could be is connection failure due to server down, upgrade in process or their server got spooked and closed the connection for security reasons. An “Unknown Email” is where the server said that the delivery failed and that the email address does not exist. This is typical of a type of false positive. An ISP will send these if they suspect the IP range to be spam. An “Attempt Rejected” is when the delivery failed because the recipient rejected the connection. Could be because the IP range has a history of spam or security protocol.

A “Relay Error” is when the delivery failed because a relaying problem took place. Either they blocked us or the range is in question. Many ISP’s use this as a false positive narrative. An Antispam System” is anti-spam technology that is blocking the verification progress. Barracuda and the like use sophisticated technology to sniff out verification companies if they are doing SMTP handshakes. An “Email Disabled” happens when the email account is suspended, disabled, or limited and cannot receive emails. A Domain Error is when the email server for the whole domain is not installed or is incorrect, so no emails are deliverable. An “ok for all” is when the email server is saying that it is ready to accept letters to any email address or “catch all”.

A “Dead Server” is when the email server is dead, and no connection to it could be established. Typical 550 bounce. A “Syntax Error” is where there is a syntax error in the email address. Like two @ signs or unwanted spaces. An “Unknown” is where the email delivery failed, but no reason was given. Often, this is what occurs with most returning messages when the ISP simply is ignoring you. False positives come from this as well. An “Accept All” means the server is set to accept all emails at a specific domain. Most antispam hosting providers use this feature to capture all messages for analytics. As you can see from above, there are dozens and dozens of steps that we need to do in order to verify and report back what happened. So before you think to yourself that you want to scrub email list free, think about what you really are getting after the process. Email marketing is hard and should be respected. Same with the process of verifying the email itself.