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 ho… (read more)
- 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:
Outgoing SMTP:
- 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.