MULE-7837: Added offset and limit parameter to email retrieving process....

... Added tests for the delete/no delete options when retrieving them.
This logic handles the case where the emails are deleted after being processed, and so there's no need to use an offset to retrieve them, but also the one not taken into account which is when they are not deleted and so they must be retrieved using an offset that depends on how many where previously retrieved. I'll add some comments and try to make this more explicit.