How Do Third-Party Email Verification Services Work?
Posted: Wed May 21, 2025 3:35 am
The process undertaken by email verification services is a multi-layered one, involving a series of checks to ascertain the authenticity and deliverability of an email address. While specific methodologies may vary between providers, the core steps generally include:
A. Syntax Validation (RFC Compliance)
The first and most basic check ensures that the iran email list email address adheres to the standard format defined by the Internet Engineering Task Force (IETF) in RFCs (Request for Comments), particularly RFC 5322 and RFC 5321. This involves checking for:
If an email fails this check, it's immediately flagged as invalid.
B. Domain Validation
This step verifies the existence and validity of the domain name associated with the email address.
DNS Lookup (A/AAAA Records): The service queries the Domain Name System (DNS) to check if the domain exists and has associated A (IPv4) or AAAA (IPv6) records, which map the domain name to an IP address.
MX Record Check: The service looks for MX (Mail Exchange) records for the domain. MX records specify the mail servers responsible for accepting email messages on behalf of a recipient's domain. If no MX records are found, it indicates that the domain cannot receive emails, and the address is likely undeliverable.
C. SMTP Connection and Mailbox Existence Check
This is one of the most crucial and complex steps, involving an attempt to connect to the recipient's mail server.
SMTP Handshake: The verification service simulates sending an email by initiating an SMTP (Simple Mail Transfer Protocol) handshake with the mail server specified by the MX records.
Recipient Verification: During this handshake, the service typically sends a VRFY (verify) or RCPT TO (recipient to) command with the email address in question. The mail server's response indicates whether the mailbox exists.
"OK" Response: Indicates the mailbox exists and is ready to receive emails.
"User unknown" or "Invalid mailbox" Response: Indicates the mailbox does not exist, confirming a hard bounce.
"Greylisting": Some servers temporarily reject unknown senders to deter spam. Reputable verification services are designed to handle greylisting by retrying the connection after a short delay to get a definitive status.
A. Syntax Validation (RFC Compliance)
The first and most basic check ensures that the iran email list email address adheres to the standard format defined by the Internet Engineering Task Force (IETF) in RFCs (Request for Comments), particularly RFC 5322 and RFC 5321. This involves checking for:
If an email fails this check, it's immediately flagged as invalid.
B. Domain Validation
This step verifies the existence and validity of the domain name associated with the email address.
DNS Lookup (A/AAAA Records): The service queries the Domain Name System (DNS) to check if the domain exists and has associated A (IPv4) or AAAA (IPv6) records, which map the domain name to an IP address.
MX Record Check: The service looks for MX (Mail Exchange) records for the domain. MX records specify the mail servers responsible for accepting email messages on behalf of a recipient's domain. If no MX records are found, it indicates that the domain cannot receive emails, and the address is likely undeliverable.
C. SMTP Connection and Mailbox Existence Check
This is one of the most crucial and complex steps, involving an attempt to connect to the recipient's mail server.
SMTP Handshake: The verification service simulates sending an email by initiating an SMTP (Simple Mail Transfer Protocol) handshake with the mail server specified by the MX records.
Recipient Verification: During this handshake, the service typically sends a VRFY (verify) or RCPT TO (recipient to) command with the email address in question. The mail server's response indicates whether the mailbox exists.
"OK" Response: Indicates the mailbox exists and is ready to receive emails.
"User unknown" or "Invalid mailbox" Response: Indicates the mailbox does not exist, confirming a hard bounce.
"Greylisting": Some servers temporarily reject unknown senders to deter spam. Reputable verification services are designed to handle greylisting by retrying the connection after a short delay to get a definitive status.