Symptoms

JIRA crashes or behaves unpredictably. Email notifications may stop being sent. Logs contain errors like:

java.lang.OutOfMemoryError: Java heap space 

Diagnosis

In addition to Java heap space error, the following will be logged in atlassian-jira-incoming-mail.log:

2020-06-16 11:30:17,600 ERROR [] Caesium-1-4 ServiceRunner MailJobRun java.lang.OutOfMemoryError: Java heap space

Cause

JIRA can get caught in a mail loop, where a notification is sent to an inbox that is then processed by a mail handler.

Workaround

1. As a temporary measure, increase JIRA's Heap Space allocation.
2. Restart JIRA
3. Configure either the Notification scheme or the Mail Handler to prevent the loop. It is generally a good idea to set bulk=forward and set a Forward Email address, to prevent mail loops between JIRA and another automated service (eg. another JIRA installation). See Handler Parameters for details on how to set the parameters for the handler.

See JRASERVER-11074 for further updates.