Порт 993 (IMAPS)

Port 993 is the standard port for Internet Message Access Protocol over SSL/TLS (IMAPS). IMAPS is a secure method for retrieving email from a mail server. Unlike its predecessor, POP3, IMAPS allows users to access and manage email directly on the server, synchronizing changes across multiple devices. It maintains a persistent connection to the server, enabling real-time updates and folder management. The protocol encrypts the entire communication session using SSL/TLS, protecting usernames, passwords, and email content from eavesdropping. IMAPS uses TCP as its transport protocol, establishing a connection to the server on port 993. Once the connection is established, the client authenticates with the server, typically using username and password credentials or more advanced authentication mechanisms like OAuth. After successful authentication, the client can retrieve, send, delete, and manage emails stored on the server.

At a technical level, the IMAPS process begins with a TLS handshake to establish a secure channel. The client initiates a TCP connection to the server on port 993. The server presents its SSL/TLS certificate, which the client verifies. If the certificate is valid, a secure connection is established using symmetric encryption. Once secured, the IMAPS protocol commands are exchanged, such as LOGIN (for authentication), SELECT (to choose a mailbox), FETCH (to retrieve email messages), STORE (to modify message flags), and EXPUNGE (to permanently delete marked messages). The use of SSL/TLS encryption ensures confidentiality and integrity, protecting the transmitted data from interception and tampering. The protocol's design allows for efficient email management and synchronization across multiple devices.

## Firewall Recommendations

Port 993 should generally be allowed for legitimate IMAPS traffic if email access is required. Block it if IMAPS is not used within the network. For incoming connections, restrict access to authorized IP addresses or networks to reduce the attack surface. Regularly update IMAPS server software to patch security vulnerabilities. Enforce strong password policies and consider multi-factor authentication to protect against brute-force attacks. Implement intrusion detection and prevention systems to monitor for suspicious activity on port 993. Ensure that SSL/TLS certificates are valid and up-to-date. Use strong cipher suites and disable older, vulnerable protocols like SSLv3 and TLS 1.0. Outbound connections from internal mail servers to external IMAPS servers should also be monitored to prevent data exfiltration.