Should port 143 be open to the internet?

Should not be public. Use IMAPS on 993 instead; plain IMAP exposes credentials.

Should not be public

Port 143 — IMAP

Mail access that leaves messages on the server and syncs across devices.

Port

143

Service

IMAP

Protocol

TCP

Security guidance

Use IMAPS on 993 instead; plain IMAP exposes credentials.

Test port 143 yourself

From your own machine, against any host (swap in your domain):

macOS / Linux — netcat

nc -vz example.com 143

Any OS — nmap

nmap -p 143 example.com

Windows — PowerShell

Test-NetConnection example.com -Port 143

open = a service answered on port 143; closed = the host replied but nothing is listening; filtered = a firewall silently dropped the probe. These test from your network — our port checker tests from the outside, the view that matters for security.

Is port 143 open on your server?

Test it from outside your network — the only view that matters.

Check port 143

Other common ports

20 · FTP data 21 · FTP control 22 · SSH / SFTP 23 · Telnet 25 · SMTP 53 · DNS 80 · HTTP 110 · POP3 123 · NTP 161 · SNMP 389 · LDAP 443 · HTTPS 445 · SMB 465 · SMTPS 587 · SMTP submission 993 · IMAPS 995 · POP3S 1433 · Microsoft SQL Server 1521 · Oracle Database 2082 · cPanel 2083 · cPanel (TLS) 3000 · Node.js / dev server 3306 · MySQL / MariaDB 3389 · RDP 5432 · PostgreSQL 5900 · VNC 6379 · Redis 8080 · HTTP alternate 8443 · HTTPS alternate 9200 · Elasticsearch 27017 · MongoDB