The port 143/TCP is used by…IMAP to view and synchronize messages stored on a mail server. It can secure the session with STARTTLS, unlike port 993 which commonly uses implicit TLS; the diagnosis must therefore distinguish between connectivity, TLS negotiation and account authentication.
What is Harbour 143 for?.
The port 143/TCP is used by IMAP to view and synchronize server-side messages. The service can offer a TLS climb with STARTTLS. The 993 port is commonly IMAP with implicit TLS. A successful network connection therefore does not guarantee the expected encryption level or the account authentication.
The diagnosis must separate DNS, transport, TLS negotiation and IMAP commands.
Transport Protocol
TCP
Safety precautions
Should we open this port in the firewall?
Avoid clear IMAP authentication on an uncontrolled network. If port 143 remains in use, impose ▼TLS when the platform allows it or migrate customers to an implicit TLS configuration on 993. An Internet exposure may be legitimate for the use of the users of the service, but must be intentional and protected by the mechanisms of email authentication.
How do I check this port?
Test port 143 first and then run the capabilities announced by the server. If ▼TLS is planned, openssl s_client -starttls imap -connect SERVER:143 helps to verify the negotiation and certificate.
- Validate DNS and connectivity for the TCI.
- Check if ▼TLS is required and accepted.
- Then check the authorized authentication methods.
- Compare with 993 if customers are configured in implicit TLS.
FAQ — port 143 / IMAP
What difference between IMAP 143 and IMAPS 993?
143 corresponds to IMAP with possibility of boroughTLS depending on the server, while 993 is commonly used for IMAP with implicit TLS.
Why port 143 answers but Outlook does not connect?.
The problem can be after the tactile: boroughTLS requirement, certificate, d method, authentication or box settings.
Can 143 be closed if 993 is active?
Yes if no customer or service depends on 143. Check usage before removing the service.