Summary

Custom email address that is configured for Jira Service Desk Project stops working for a period of time and resumes after.

At the same time, incoming email processing works fine if you configure this custom email address via Jira Mail Handler:
https://<instance_hostname>/secure/admin/IncomingMailServers.jspa 

This happens because one of the configured custom emails in Jira Service Desk is suffering from overload - sudden spam surge, auto-reply loops.

As a result, none of the Jira Service Desk custom emails in the instance work for a period of time.

Customer Impact

Jira Service Desk is not processing incoming emails for all custom email addresses within the instance.

Steps to Reproduce

1. Go to email settings in a JSD project and assign the custom email address
2. Make your Jira Service Desk publicly accessible (anyone can raise a request)
3. Create some circumstances to have inbox of the mailbox being spammed (tested with mailbox having 10k incoming emails)
4. Jira Service Desk will stop processing any incoming emails for this mailbox and any other configured for JSD projects.

In fact Jira Service Desk continues to process incoming emails, however cannot do it fast enough to go through all the volume of 'spammed' mailbox.

Expected Results

1 overloaded mailbox should not affect other JSD configured mailboxes

Actual Results

Overloaded mailbox affects processing of incoming emails for all JSD custom mailboxes

Workaround  

1. Disable affected JSD mailbox via JSD email request settings (remove mailbox from 'custom email address')
2. Clear all the spam/unwanted emails from Inbox
3. Switch JSD mailbox back