Email List Verification Process Explained

My last article was all about email list validation. Is there a difference betweenemail validation and email verification? Yes there is. Email validation fixes formatissues and syntax errors while email verification reports if an email is valid (doesthe mailbox exist) and if not, lists the reason for the return path. Email validationfixes and/or removes duplicates, disposables, departmentals, botclickers, falsepositives, slow responses, forwarders, format errors, unicode characters and insome cases, checks the mail exchange record for numerous warning signs.

Email verification is all about non-return email deliverability by avoiding autoresponders that can hurt your sender reputation. Valid emails without a return-pathare favorable with email administrators and email service providers. The more

emails you send, the more likely you will encounter bounces (hard or soft),vacation emails, challenge responses, replies from list servers or feedback reports.

An email verification service will use these steps in order to achieve trueverification (not in order and not all verification companies do these step by step):

Mail advertisements to your list. You get the best results when you send a directSMTP handshake with content. This could agitate your subscribers because you arenot in control of the content being sent.

Appending database. A collection of emails with the last known deliverability datewhich is updated often.

Check social media email addresses. Social Media email addresses tend to be theunique email address of the holder. Some verifiers have a list of Facebook orTwitter accounts and append to that.

Send a blank email via SMTP (simulate a direct message delivery) to authenticatethe user.

Establish a connection to the mail server via an SMTP protocol (based on TCP). Byusing connection-oriented dispatch service packaging to establish the connectionwith hello messages, the sender’s address is transmitted and the receiving serversubmits the message from this address to be accepted. Then the addressee’s addressis transmitted.

Emulate a second message dispatch. No message is actually sent during the emailavailability check. This process establishes the connection with the mail server,sends a hello message, transmits the sender’s address (options/sender) to pretendthere is a message and then transmits the subscriber’s mailbox address (an emailaddress being checked). As soon as the receiving server confirms or denies therequested mailbox availability, the email verification tool disconnects.

DNS Response times from two locations (Timeouts). If the verifier does not receivea response from a DNS server during a specified period of time (1 – 2 seconds),verifiers will make new attempts using another DNS gateway.

Send through different ports in case of roaming or receiver scenarios. In example, ifport 25 is intercepted, then tunnel to another transparent proxy or through port 587and/or other options.

Enhanced mail system status codes check. Success (valid email) specifies that theDNS is reporting a positive delivery status. Detailed status codes may providenotification of transformations required for delivery checks.

A persistent transient failure is when the message sent is valid, but persistence ofsome temporary condition has caused abandonment or delay of attempts to send themessage. If the code accompanies a delivery failure report, sending in the futuremay be successful.

A permanent failure is when the email is not likely to be resolved by resending themessage in the current form. Some change to the message or the destination must bemade for successful verification.

Querying the mail exchange record. Bad MX emails have slow response times, 4xxerrors, full load distribution, the mail exchange isn’t configured correctly, incorrectport numbers, has no backup server, is parked or the website doesn’t follow typicalmail exchange setup standards.

Here are the reporting parameters of email verification after the above steps havebeen completed by an email list cleaning service (not in order and not allverification companies do these step by step):

Valid 250The email passed all verification questions and is considered a true deliverable.

Hard Bounce 550The email server was temporarily unable to deliver your message to thesubscriber’s email address because the subscriber’s address does not exist.

General Bounce

The email server could not deliver your message, but the exchange could notdetermine a specific reason for the bounce. The bounce message from thesubscriber’s server was widespread.

Soft BounceThe email server was temporarily unable to deliver your message to thesubscriber’s email address because of Internet outage, interruption and/orconnection timeout issues.

Soft Bounce DNS FailureThe email server is temporarily unable to deliver your message to the subscriber’semail address because of a DNS connectivity issue or incorrect configuration.

Soft Bounce Mailbox FullThe email server is temporarily unable to deliver your message to the subscriberbecause the subscriber’s email box is full.

Soft Bounce Message Size Too LargeThe email server could not deliver your message to the subscriber because themessage size is too large.

Transient BounceThe email server temporarily cannot deliver your message, but it is still trying.

Slow ResponseThe email server temporarily cannot deliver your message, but it is still trying.

Mail Block Relay Denied 551Indicates that the subscriber’s email server is blocking email from our email serverwhether for spam or other reasons.

General Mail Block 550Indicates that the subscriber’s email server is blocking email from our email serverwhether for spam or other reasons.

Mail Block Known SpammerIndicates that the subscriber’s email server is blocking your email because itbelieves you are a spammer.

Mail Block Spam Detected 550Indicates that the subscriber’s email server is blocking your email because themessage appears to have content that looks like spam.

Auto ReplyAn automatic response from the subscriber sent to your server, which could be outof office or a vacation message.

ForwarderReport back any disconnected user, roaming or greeting card scenario (forexample, a user can instruct Gmail to forward messages to a different emailaddress. The sender is not necessarily aware of that) called “Forwarder”.

Bounce With No Email Address (BN)Determined that the message was a bounce, but it could not resolve the originalemail recipient email address. False positive.

Mail Block Attachment Detected (MBAD)Indicates that the subscriber’s email server is blocking email from your emailserver because the email message contained an attachment.

Mail Block – Relay Denied (MBRD) 551Indicates that the subscriber’s email server is blocking email from your emailserver.

Challenge response spam filteringSpam filter that automatically sends a reply with a challenge to the sender toperform some action to assure delivery of the original message.

List Server Replies (SMTP Replies)

A program that handles subscription requests for a mailing list and distributes newmessages, newsletters, or other postings from the list’s members. (A list servershould not be confused with a mail server, which handles incoming and outgoinge-mail for Internet users.)

Feedback ReportsA mailbox provider forwards the complaints originating from their users to thesender’s organizations.

False Positive 550User account is not there, or they turned on/off a feature that allows for non-listedusers to pass through.

Email verification companies will use their own code to determine the reportingabove. At times, verification cannot get responses from the subscriber’s emailserver due to mail server configurations. Administrators make changes to theirmail servers daily as they monitor traffic from the same source or ranges. They setalerts for anything suspicious especially when a range of IP’s are asking questionswithout sending responses. The email verification process is a delicate andexpensive procedure if done right. In this case, you definitely get what you pay for.