When adding a mail channel, the message "Unable to create new mail channel due to connection duplication" appears

Summary

When adding a mail channel to a request type in JIRA Service Desk, the following error gets displayed in the screen:

Unable to create new mail channel due to connection duplication. Provided mail connection definition is currently used by another mail channel.

Steps to Reproduce

1. Create a new issue type in JIRA
2. Create a new request type in Service Desk and link it to the issue type of step 1
3. Add a mail channel for the request type created in step 2
4. Remove the issue type created in step 1 from the project configuration
5. Add a new mail channel for another request type in a Service Desk using the same mail credentials as in step 3

Expected Results

The mail channel gets added

Actual Results

The following error shows in the UI after choosing the request type to which the mail channel should relate:

Unable to create new mail channel due to connection duplication. Provided mail connection definition is currently used by another mail channel.

Workaround

1. Navigate to the email settings of your instance by going to baseurl/secure/admin/SDMailInfo.jspa.
   Here you should be able to find the email address already being present that you are trying to add
2. Use the delete option to remove the channel from the instance
3. Recreate the mail channel from within the service desk