Issue : Ability to Create issues via incoming mail handler with required fields and custom fields

Summary :
Presently it's not possible to create issues via mail handler if the project has any required field in the create screen.
It fails and issues don't get created
Also there is no way where we can add any entry to a custom field which is not mandatory via mail handler
It would be great if there is any feature for the same

Suggestion
Introduce an option with mail handler setup to fill in any other field we would like while setting my incoming mail handler for a project