Internet-Security.com TCP port 587 details

TCP port 587 is the standard mail submission port for SMTP with STARTTLS (RFC 6409).
Email clients use it to send mail to servers like Gmail (smtp.gmail.com:587), Microsoft 365/Outlook (smtp.office365.com:587), Yahoo Mail, Zoho Mail, and iCloud Mail.
On‑premises mail servers expose 587 via Microsoft Exchange Server, Postfix, Exim, Sendmail, and qmail for authenticated client submission.
Managed email providers including Amazon SES, SendGrid, Mailgun, and SparkPost accept SMTP submissions on 587.
Many deployments enable the submission service on 587 through Dovecot or Courier as part of a full mail stack.
Email security appliances such as Fortinet FortiMail and Cisco Secure Email (formerly IronPort/ESA) listen on 587 for client SMTP submission.
Desktop and mobile clients like Apple Mail, Microsoft Outlook, Mozilla Thunderbird, and Mutt default to 587 for authenticated SMTP with STARTTLS.
Security: attackers often brute‑force SMTP AUTH on 587 or abuse misconfigured relays, and vulnerabilities in software like Exim have been exploited when exposed on this port.

TCP 587