IMAP/SMTP server connected, but receives and send fails

## Thunderbird connects to my IMAP/SMTP server but neither receives nor sends mail I am having a problem with Thunderbird on Windows with a custom-domain email account hosted by Advika Web. ### Account Email address: `connect@synergyappstudio.com` Mail hosting provider: Advika Web The mailbox and password are confirmed to be valid because I can successfully log in to the provider's webmail using the same email address and password. ### Server settings provided by the hosting provider Incoming IMAP: * Server: `mail.synergyappstudio.com` * Port: `993` * Connection security: SSL/TLS * Authentication: Normal password * Username: `connect@synergyappstudio.com` Outgoing SMTP: * Server: `mail.synergyappstudio.com` * Port: `465` * Connection security: SSL/TLS * Authentication: Normal password * Username: `connect@synergyappstudio.com` ### What happens in Thunderbird Thunderbird shows: > Connected to mail.synergyappstudio.com However, incoming messages are not downloaded and outgoing messages cannot be sent. The SMTP error I received was: > The connection to Outgoing server (SMTP) mail.synergyappstudio.com timed out. ### Connectivity tests I tested the server from Windows PowerShell. Port 993: `Test-NetConnection mail.synergyappstudio.com -Port 993` Result: > RemoteAddress: 103.69.196.146 > RemotePort: 993 > TcpTestSucceeded: True Port 465: `Test-NetConnection mail.synergyappstudio.com -Port 465` Result: > RemoteAddress: 103.69.196.146 > RemotePort: 465 > TcpTestSucceeded: True Therefore, both TCP ports are reachable from my computer. ### TLS tests I also tested the actual TLS handshake rather than just TCP connectivity. TLS 1.2 against IMAP 993 failed with: > Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. TLS 1.0 against IMAP 993 produced the same result: > Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. I also tested the TLS handshake against SMTP 465 and received the same "connection was forcibly closed by the remote host" result. ### Comparison with Outlook There is an important comparison: The same mailbox **successfully connects and authenticates in Classic Outlook** using the same server and credentials. However, I am using Microsoft Office Home & Student, so Classic Outlook is not available to me as a practical permanent solution for this business email account. Microsoft's **New Outlook** also fails to add the account and displays: > Sign in failed. Please try again in a few minutes. You may need an app password. The mailbox does not use Microsoft 365 authentication. It is a conventional hosting-provider IMAP/SMTP mailbox. ### Thunderbird troubleshooting already attempted I have: * Confirmed the password works through webmail. * Confirmed the supplied IMAP/SMTP server names. * Confirmed ports 993 and 465 are reachable. * Confirmed SSL/TLS settings. * Used Normal Password authentication. * Used the full email address as the username. * Tried Thunderbird with the supplied IMAP/SMTP settings. * Reduced **Maximum number of server connections to cache** from the default 5 to 3 and then to 1. This did not resolve the problem. * Restarted Thunderbird after changing the connection-cache setting. * Tried Thunderbird's connection logging, but the generated log files remained 0 KB, so no useful log was produced. ### Additional observation Thunderbird displays "Connected to mail.synergyappstudio.com", but the account does not actually synchronize incoming mail. The provider's webmail works normally, and Classic Outlook works with the same mailbox. ### What I would like help determining Could you please help determine whether this is: 1. A Thunderbird IMAP/SMTP compatibility issue with this particular mail server; 2. A TLS negotiation issue; 3. A Thunderbird configuration/profile issue; 4. A Windows/security-software interaction; or 5. Something specific to the mail server's IMAP/SMTP implementation? In particular, I would like to understand why Thunderbird can establish the connection but cannot complete the IMAP/SMTP communication, while Classic Outlook works with the same server, ports and credentials. I can provide Thunderbird version information, Troubleshooting Information, screenshots of the account configuration, or any additional diagnostic information you need.