STARTTLS Studio
A DNS Studio tool
Tester
Full report
Guides
About
Studio tools
DNS
Check DNS records and propagation
DNSSEC
Check DNSSEC signing and validation
DKIM
Check email signing records
BIMI
Check brand logo records
TLS
Inspect TLS versions and chains
SSL
Check certificate status and expiry
Propagation
Check global DNS propagation
MTA-STS
Check inbound mail TLS policy
HSTS
Check HSTS and preload status
STARTTLS
Test SMTP STARTTLS encryption
CNAME
Follow CNAME chains and aliases
Redirects
Trace HTTP redirects and status
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STARTTLS Studio
Guides
Practical, plain-English explainers to go with the tool.
What is STARTTLS?
How mail servers upgrade to an encrypted session.
STARTTLS vs implicit TLS
Ports 25, 465 and 587 explained.
STARTTLS stripping
The downgrade attack, and why MTA-STS/DANE exist.
Reading an MX record
Preferences, backup MX, and null MX.