Can I tune the queue size table?
When transactional emails are queued, they will be added to the queue_item__c table. Queue items are cleared out quite quickly, so in most cases, it should be empty or have very little data, which will eventually be cleared out. There is a setting that will check the table and clear out any old data which is, by default, older than two days. This can be tuned from our maintenance tab. Once there, click on the cog to open the governor limits modal. Then, change the settings as indicated -