TCP 2525
Synopsis
- TCP port 2525 is commonly used for SMTP submission (SMTP with STARTTLS/TLS) as an alternative to ports 25/587 when those are blocked by networks or cloud providers.
- Real-world services that accept SMTP on 2525 include Twilio SendGrid, Mailgun, SparkPost, Mailjet, Postmark, Mandrill (Mailchimp Transactional), SocketLabs, SMTP2GO, and Elastic Email.
- Platforms like Heroku specifically recommend using 2525 for SMTP with add-ons such as SendGrid or Mailgun because many dyno networks restrict port 25.
- Security note: attackers sometimes scan port 2525 for misconfigured SMTP relays to send spam, though it isn’t tied to a unique exploit protocol.
Observed activity
Last 30 days
Detailed chart