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Courier IMAP SSL configuration : How to install?

Courier IMAP SSL configuration is a sure-shot way to enhance mail server security.

The SSL certificate makes all the email transactions secure and easily prevents eavesdropping.

However, the installation of SSL on Courier IMAP involves a series of steps that often go wrong.

That’s why we often get requests from our customers to install courier IMAP SSL and fix related errors as part of our Server Management Services.

Today, we’ll explain how our Support Engineers install courier IMAP SSL and help to fix related errors.


How to install the SSL in courier IMAP?

The Courier IMAP Mail Server is a mail transfer agent that provides mail services for regular operating system accounts.

The proper installation of the courier IMAP SSL includes generating a CSR certificate, installing the purchased certificate, testing the SSL installation.

Let’s see how our Support Engineers installed the SSL certificate in courier IMAP.


Generating CSR certificate

The CSR or certificate signing request is a block of encoded text that is given to a Certificate Authority when applying for an SSL Certificate. To pass the SSL validation we need to create CSR and send it to  SSL certificate providers.

1. To generate the CSR, we connected to the server, and then we created the SSL directory.

mkdir -p /usr/local/ssl

cd /usr/local/ssl

Then from the prompt, we ran the following command.

openssl req -new -nodes -keyout your_domain_name.key -out your_domain_name.csr

This command will generate the CSR request and the private key, which is essential while installing the certificate.

2. We asked the customer to fill the personal details as follows:

  • Common Name: enter the fully-qualified domain name of the website (e.g., or
  • Organization: The legal name of the organization/company includes Inc., LLP., Pvt, Plc. Ltd. SARL., etc
  • Organizational unit: The name the department within the organization.
  • City/locality: Location of the city or town
  • State/Province: The state in which your organization located
  • Country: The code of the country

The CSR and private Key files will be saved to the current directory. The Private Key file should be kept safe as it will be essential while installing SSL.

3. We then Opened a text editor and copy the CSR with the entire text including the BEGIN and END tags when ordering the SSL Certificate.

4. After generating the CSR certificate, we submitted the CSR to the SSL certificate providers (CA) account and get the final certificate.


Installing Certificates

We will unzip the received CA certificate, and after that we will assist in installing the certificate. Then we add the certificates to the corresponding files, which has been created under the directory /usr/local/ssl. Now we created the following four files and save it.

  • /usr/local/ssl/intermediate.crt
  • /usr/local/ssl/your_domain_name.crt
  • /usr/local/ssl/your_domain_name.csr
  • /usr/local/ssl/your_domain_name.key

In Courier-IMAP, it is necessary that the certificate and the private key should be present in a file. For this, our Dedicated Engineers created a new file /usr/local/ssl/your_domain_name.pem with .pem extension and combined the files  /usr/local/ssl/your_domain_name.key and /usr/local/ssl/your_domain_name.crt

cat /usr/local/ssl/your_domain_name.crt /usr/local/ssl/your_domain_name.key >> /usr/local/ssl/your_domain_name.pem


Configure Courier IMAP SSL Certificate

Finally, we opened the IMAP configuration file /usr/local/etc/courier-imap/imapd-ssl.

Inserted the following line into the configuration:


Also, we make sure that the certificate file has only minimal rights that only the root user can read all files located in the SSL folder.

chmod 600 /usr/local/ssl/your_domain_name.pem

chown root.root  /usr/local/ssl/your_domain_name.pem

After that we restarted the Courier IMAP server:

/usr/local/etc/rc.d/courier-imap-imapd-ssl restart

Now we have successfully installed the SSL Certificate on Courier IMAP Server.

To test the installation we used the following command:

openssl s_client -connect your_domain_name:993

An OK response will appear as:


How we fixed errors related to Courier IMAP SSL

At Bobcares, where we have more than a decade of expertise in managing servers, we see many customers face problems related to Courier IMAP SSL configuration.

Now, let’s see the major reasons for this Courier IMAP SSL related errors and how our Support Engineers fix the top errors.


Configuration errors with Protocols

Often connecting to a mail server over SSL via email clients like Outlook fails with error:

Log onto incoming mail server (IMAP): Your server does not support the connection encryption type you have specified. Try changing the encryption method.

This happens when the Protocol version does not match with the one used in the Courier IMAP SSL configuration.

Our Security Engineers always recommend disabling outdated protocols. Restricting TLS on the server reduces the number of email servers that could connect on to the server.

However, after weighing customer requirement and server security, we had to adjust the configuration to:


Finally, we restarted Courier services using:

# service courier-imaps restart

Wrong SSL certificate

Similarly, the wrong SSL certificate on the mail server hostname also can create errors for users. Ideally, all email client users should be connecting to the correct hostname that has a proper SSL certificate. Else, they will receive an SSL name mismatch error.

When customer report mismatch error, our Dedicated Engineers check and confirm the certificate settings from the server. For instance, in Plesk Server, it clearly shows up under Tools & Settings >> SSL/TLS Certificates

courier IMAP SSL configuration


[Need more help to solve Courier IMAP SSL errors?- We’ll help you]



In short, Courier IMAP SSL provides reliable and secure email communication on all major server types. Today, we saw how our Support Engineers ensure a proper Courier IMAP SSL configuration and fix related errors.


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