STARTTLS Checker

Check if email servers support STARTTLS for SMTP, IMAP, and POP3

About STARTTLS Email Encryption

STARTTLS is a protocol command that upgrades an existing plaintext email connection to an encrypted TLS connection on the same port. It is supported by SMTP (port 587), IMAP (port 143), and POP3 (port 110) protocols. Without STARTTLS, email messages and credentials are transmitted in plaintext, making them vulnerable to interception. Our STARTTLS Checker tests all three protocols to give you a complete picture of your mail server's encryption capabilities.

How to Use

Enter the mail server domain name (e.g., mail.example.com).
Click Check STARTTLS to test all three email protocols.
Review the STARTTLS support status for SMTP, IMAP, and POP3.
Read the summary for an overall assessment of the server's email encryption.

Use Cases

Email Security Audit: Verify that your mail server enforces STARTTLS for all incoming and outgoing email connections.
Server Configuration Testing: Confirm that SMTP, IMAP, and POP3 services are properly configured to offer TLS upgrades.
Compliance Verification: Meet regulatory requirements (GDPR, HIPAA, PCI-DSS) that mandate encryption of email in transit.
Vendor Assessment: Evaluate third-party email providers to ensure they support STARTTLS before migrating your services.

Frequently Asked Questions

SMTPS (SMTP over TLS) uses a dedicated port (465) for encrypted connections from the start. STARTTLS uses the standard port (587 for SMTP) and upgrades the connection to TLS after the initial handshake. STARTTLS is the modern, standards-compliant approach.

Yes, STARTTLS is vulnerable to downgrade attacks (STRIPTLS) where an attacker strips the STARTTLS capability advertisement. The recommended mitigation is to enforce MTA-STS (SMTP MTA Strict Transport Security) and TLS reporting policies.

The tool tests STARTTLS on SMTP (port 587), IMAP (port 143), and POP3 (port 110). These are the standard ports where STARTTLS is used to upgrade plaintext connections to encrypted ones.

Tips & Best Practices

•Verify STARTTLS is properly configured for email protocols
•Test STARTTLS upgrade from plaintext to encrypted connection
•Monitor STARTTLS availability for email server security
•Configure mandatory TLS for email encryption when possible

Technical Details

Protocol: STARTTLS upgrade support for SMTP, IMAP, POP3
Upgrade: Plaintext to TLS upgrade mechanism
Security: STARTTLS stripping attack protection
Output: STARTTLS support status with configuration recommendations