Check to see if the message reaching the e-mail account . Have the mail server administrator confirmed that e-mail sent to the JIRA application account is successfully reaching the account's Inbox. ( ask Joost van Hemert, René van der Pal, Bianca van der Meer)
Check that the Create Or Comment Handler service configured correctly in the JIRA application. Please review Creating Issues and Comments from Email to assess this.
Check that the permissions are set properly. Does the user submitting the issue have Create Issue permissions in thePermission Scheme? User need to be a member of group: YMEUACJiraIssueEmailCreators
Run a test on for Inbound mail server to see if any error is generated.
Go to Jira → System - Mail
Select Edit
Click on: Test connection Error notification will be shown this need to be forwarded to Infra team to investigate.
In most cases the exchange server need to be rebooted and services need to be checked.