TCP 143
Synopsis
- TCP port 143 is the default port for the Internet Message Access Protocol (IMAP/IMAP4) used by email servers.
- Common IMAP server software listening on 143 includes Dovecot, Cyrus IMAP, Courier-IMAP, UW IMAP, Microsoft Exchange Server (IMAP service), hMailServer, Zimbra, and Kerio Connect.
- Microsoft 365/Exchange Online supports IMAP on 143 with STARTTLS, and many hosting providers (e.g., cPanel/WHM with Dovecot) expose this port for customer mailboxes.
- Email clients such as Microsoft Outlook, Mozilla Thunderbird, Apple Mail, Evolution, and mutt connect to servers on 143 for IMAP (often upgrading to TLS via STARTTLS).
- IMAP proxies/load balancers like NGINX mail proxy and F5 BIG-IP LTM commonly accept client connections on 143 and forward them to backend mail servers.
- Security note: Port 143 is frequently targeted for credential brute-force and has seen IMAP server vulnerabilities (e.g., CVEs in Cyrus IMAP and Dovecot); using it without STARTTLS can expose passwords in cleartext.
Observed activity
Last 30 days
Detailed chart