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The Courier IMAP server requires an SSL certificate for encryption and secure communication. To obtain an SSL certificate, you first need to generate a CSR (Certificate Signing Request) file which contains information about the server and domain. The Certificate Authority (CA) verifies the details and issues an official SSL certificate after receiving the submitted CSR. Once the certificate is installed on the Courier IMAP server, it will enable SSL encryption for IMAP, POP3 and SMTP protocols and secure email communications.
Generating a CSR for Courier IMAP involves a few simple steps – creating the SSL certificate directory, generating the CSR and key files using OpenSSL, moving them to the Courier SSL directory, enabling SSL support in the Courier configuration, restarting the Courier service and then submitting the CSR to obtain and install the SSL certificate.
openssl req -new -newkey rsa:2048 -nodes -out mydomain.csr -keyout mydomain.key
Using this command, you will generate two files:
ssl=on ssl_cert=/etc/courier/ssl/mydomain.csr ssl_key=/etc/courier/ssl/mydomain.key
Courier IMAP will now be using SSL encryption for communication.