An SMTP check is a process used to verify whether an email address can receive messages by communicating with the recipient’s mail server through the Simple Mail Transfer Protocol (SMTP). It is one of the most advanced steps in email validation.
What Is SMTP Check?
SMTP check involves establishing a real-time connection with the mail server responsible for a domain to confirm if the recipient’s mailbox exists and can accept messages. Unlike syntax checks or domain checks, which only validate structure and DNS records, SMTP verification interacts with the actual email server for accuracy.
For example:
- john.doe@example.com might pass syntax and domain checks, but if the mailbox does not exist, an SMTP check will reveal this.
- SMTP checks reduce hard bounces by confirming that the mailbox is active before sending an email.
How Does SMTP Check Work?
SMTP verification works by simulating the initial stages of sending an email, without delivering an actual message. The steps include:
- Performing a DNS query to retrieve MX records for the domain.
- Connecting to the mail server using SMTP commands.
- Using commands like HELO, MAIL FROM, and RCPT TO to verify if the server acknowledges the recipient address as valid.
- If the server responds with a positive code (250 OK), the address is considered valid; if it returns an error (such as 550 No such user), the email is invalid.
This process is more resource-intensive than syntax or domain checks, but it provides higher accuracy.
Why Is SMTP Check Important?
SMTP checks are critical for reducing undeliverable emails and improving sender reputation. Key benefits include:
- Accuracy: Confirms the mailbox actually exists.
- Deliverability: Avoids sending campaigns to inactive or fake email addresses.
- Reputation protection: Reduces hard bounce rates, which can harm IP and domain reputation.
- Cost efficiency: Saves resources by preventing emails from being sent to invalid mailboxes.
Common Use Cases
SMTP checks are widely implemented in:
- Email validation services: As the final stage, after syntax and domain checks, for precise verification.
- Bulk email cleaning: Before sending large-scale campaigns to minimize bounce rates.
- Onboarding processes: Platforms use SMTP checks to validate email addresses during user registration to block fake or invalid accounts.
- Fraud prevention systems: Detecting invalid or disposable email addresses in real time.
FAQs About SMTP Check
What does an SMTP check do?
It connects to the recipient’s mail server and verifies if the mailbox exists without sending an actual email.
Does SMTP check send a real email?
No. It simulates an email transaction without delivering a message, ensuring the mailbox is valid without user disruption.
Is an SMTP check 100% accurate?
Not always. Some servers use catch-all settings or disable responses for privacy, so advanced email validation tools use additional methods to handle these cases.
