1. Which ports matter

      • 25 — server-to-server SMTP (often blocked by cloud providers)
      • 587 — mail submission with STARTTLS (recommended for apps/clients)
      • 465 — SMTPS (implicit TLS submission)
      • 143/993 — IMAP / IMAPS for reading mail
      • 110/995 — POP3 / POP3S if still used

2. Check if the provider blocks port 25

      • Many VPS brands block outbound 25 by default to stop spam
      • Open a support ticket and request SMTP port 25 unblock if you need direct MX delivery
      • Until then, use authenticated submission (587/465) through an allowed relay/SMTP provider

3. Open ports with UFW (Ubuntu)

      • sudo ufw allow OpenSSH
      • sudo ufw allow 25/tcp
      • sudo ufw allow 465/tcp
      • sudo ufw allow 587/tcp
      • sudo ufw allow 993/tcp
      • sudo ufw enable
      • sudo ufw status

4. Open ports in cloud security groups

      • Log into your VPS provider panel
      • Edit firewall / security group for the server
      • Allow inbound TCP 25/465/587/993 from required sources
      • For submission ports, consider restricting by IP when possible

5. Test from outside

      • From another network, test: telnet mail.yourdomain.com 587
      • Or use online port checkers for 25/465/587
      • Check mail service is listening: sudo ss -tulpn | grep -E '25|465|587'

6. Security notes

      • Never run an open relay
      • Require authentication on 587/465
      • Use TLS and strong passwords or tokens
      • Monitor logs for abuse

7. Sending campaigns

Once ports and SMTP auth work, configure those SMTP accounts in Px Mailer for campaign sending, rotation, and tracking. Px Mailer: https://pxtoolx.com