Issue Summary

Jira raises ticket with incorrect priorities, even with priorities that are not even available in the project priority scheme when incoming mail handler is configured for outlook and mails were sent with HIGH and LOW importance flags.

Steps to Reproduce

1. Create a Jira instance and configure incoming mail handler using outlook.
2. Create a project priority scheme as shown below:
   
3. And make Global priority list as below:
   
4. The Priority table in the database will show the sequence as below:
   

For mail with LOW importance flag:

When a mail with LOW priority flag is read, Jira always creates it with the lowest priority available in the priority table. It does not check whether the priority is available in the project priority scheme or not. 
For example, when priorities are set like above, the issue created is as below:

Bottom is not the priority that is available in the project priority scheme and Jira always chooses the priority that has lowest sequence in the Priority table.

For mail with HIGH importance flag:

For mail sent with High Importance flag from outlook, the issue is created with TOP priority which again is unavailable in the project priority scheme. Also, unlike with Low importance flag where lowest priority is always chosen, here we couldn't identify any pattern. The behavior is quite unpredictable and one can notice it if they change the sequence in the global priority list.

When no flag is set in mail:

The behavior is correct in this case and the default priority set in the project priority scheme is picked to create the issue.

Expected Results

When the mail sent from outlook has HIGH importance flag set, the Jira issue should be created with the Highest priority available in the project priority scheme irrespective of its sequence in the global priority list.
Likewise for mail with LOW importance flag, the issue should be created with the lowest priority available in the project priority scheme.

Actual Results

Actual results are explained above.

Workaround

Possible workaround is to create the automation rule which should trigger in the issue creation. Users can check for certain conditions to confirm if the issue is created due to incoming mail setup and then use action of Edit fields and set the correct priority.

NOTE: A similar bug was also reported earlier https://jira.atlassian.com/browse/JRASERVER-75490 this only reports the problem partially. It reported issue with the LOW importance flag. However the problem is with both LOW and HIGH importance flags. Low importance has set pattern that it chooses the lowest from global list, HIGH importance has no pattern (or not identified while creating this bug) and the behavior is unpredictible.