Steps to Reproduce

1. Create a sandbox project.
2. Setup Incoming Mail handler for issue creation within the sandbox project.
3. Send an email to trigger the incoming mail handler.
4. Observe the priority for the newly created issue on incoming mail.

Expected Behavior

Issue is created with the default priority defined in the Priorities Scheme.

Actual Behavior

Issue is created with the priority defined in the middle of the entire Priorities list.
Reference: http://<base-url>/secure/admin/ViewPriorities.jspa

Even number

If it's even number, it will select the nth priority returned by the total number divided by 2. In the following example, Critical priority will be selected.

Odd Number

If it's odd number, it will select the middle priority. In the following example, Fun priority will be selected.

Priority Not Defined in the Priorities Scheme

If the priority is not defined in the associated Priorities Scheme, it will force enter the issue type as <Priority> (Not Available).

Notes

Another variant is that if an email is sent with the "high priority" flag, it creates the request with one of the highest priorities using Default Priority Scheme instead of custom priority scheme. This is not solved by any of the workarounds.

Workaround

• You can rearrange the order of the priorities to set the one you want as default to be in the middle on the global list of priorities at Jira Administration > Issues > Priorities.
  OR
• You can use the completely free add-on Workflow Enhancer, which adds Universal postfunction to workflows that allows you to evaluate values from fields, and you can use this in the Create transition, adding a post function to evaluate if the priority is out of the project's Priorities, and to set the priority to the one you want as default. For example, setting the result of the evaluation as FALSE, from the following, should do the trick: {code} {Priority}
  == "Critical" || {Priority} == "Major" || {Priority} == "Minor" || {Priority} == "Trivial" || {Priority} == "Blocker" {code}