Can I use my website's SSL certificate for postfix and dovecot for secure connection?
In general yes. But the names you use to access the mail servers need to be part of the certificate too. So if the certificate only covers www.example.com but you want to use mail.example.com then this will not work.
I have .crt and .key files. Should I convert them into ....
I had a similar problem with Thunderbird and Dovecot after changing old certificate to new.
When I try connect to the Dovecot, I couldn't accept the new certificate on Thunderbird v 78.7.1 (32 bits) and I was a message in the dovecot log:
TLS: SSL_read() failed: error:14094412:SSL routines:SSL3_READ_BYTES:sslv3 alert bad certificate: SSL alert number 42
You have to add the option ssl_verify=no to the baseurl parameter.
So if you do not want to check the URL of the offical sources you can use:
# WARNING: Use this option only if you know what you do
Sorry for troubling you all, not sure which part finally made it works, after clearing HSTS plist and browser history and reboot, now it works. I have also confirmed that two users with same MacOS version works, only my Macbook and another colleague's Macbook had the issue. Seams because of we manually registered other Root CA which has same name.
If I understand correctly you are trying to get a client to access a web-server like this:
(Client) --- VPN --> (VPN Server) --- LAN ---> (Webserver)
Suspect your problem is that IPv4 forwarding is not enabled or there is a firewall rule blocking the packets. Of the two IPv4 packet forwarding is the more common problem.
Note that "pinging the ...
In case someone lands here and your certificate is issued with OCSP must staple you have to disable that feature in Thunderbird because Dovecot (and Postfix) probably never will support it.
Go to the Thunderbird Settings - General - scroll to the Bottom and click "Config Editor..." - accept the risk and search for the following value: