Free STARTTLS Checker

The STARTTLS Checker tool helps you verify, debug, and optimize your email authentication and DNS configuration. Proper email authentication (SPF, DKIM, DMARC) is essential for email deliverability — without it, legitimate emails may be marked as spam or rejected. This tool gives you instant, accurate results for any domain with no sign-up required.

Email authentication directly determines whether your emails reach the inbox or land in spam. SPF verifies the sending IP is authorized, DKIM proves the message was not tampered with, and DMARC enforces these policies and provides reporting. Gmail and Yahoo now require valid DKIM and DMARC for bulk senders. Missing or misconfigured records significantly increase spam classification rates across all major email providers.

DNS changes typically propagate within a few minutes to 48 hours, depending on the TTL (Time-to-Live) value of the original record and how aggressively DNS resolvers cache records. Lower TTL values (300-3600 seconds) speed up propagation. Use our DNS Propagation Checker to see current record values across global resolvers in real time without waiting for local cache to expire.