What is an SMTP port? A Clear Guide

SMTP uses port 587 (submission with STARTTLS), 465 (implicit TLS) or 25 (server-to-server). Apps should use 587 or 465 with authentication.

Why it matters

Knowing an SMTP port helps you build reliable sending. See the email API quickstart.

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, a REST API, and an AI watching deliverability — and it welcomes senders SES, SendGrid and Mailchimp reject, from $8. Run the free checker or see plans.