What is STARTTLS? A Clear Guide

STARTTLS upgrades a plaintext SMTP connection to an encrypted TLS one. It protects mail in transit but can be stripped, which is why MTA-STS exists.

Why it matters

Knowing STARTTLS helps you send mail that lands in the inbox. See the deliverability checklist.

How Rainmail helps

Rainmail sends from your own domain on a dedicated, isolated IP with SPF, DKIM, DMARC, reverse-DNS and managed warm-up handled for you, plus an AI watching list health and deliverability — and it welcomes senders SES, SendGrid and Mailchimp reject, from $8. Run the free checker or see plans.