@vicbis . Telnet is handy to check network path and if port is open. I wasn't suggesting to use the insecure ports.   4. On Windows telnet to secure ports, I get a blank screen indicating a TCP session has started. Control A ends the session back to command prompt. Is there any firewall that might be blocking port 993? How are you with packet capture software, eg. Wireshark? Shows how far the connection gets.   Telnet operation: client sends SYN to host host sends ACK + SYN to client client sends ACK TCP session has started.   On secure port, the mail client continues with CLIENT HELLO Host sends SERVER HELLO SSL handshake occurs and session runs encrypted.   ... View more