HP ALM 12.0.1 ALM Notifications not working

Hi,

 For the last couple of days,i see the the email notification in HP ALM 12.0.1 stopped working.

 SiteAdmin console has "Send Mail Automatically" checkbox checked and no changes in site configuration

Tried sending it manually, it works.

Referring to autoemails resulting in changes to Defects like Assigned to, Detected by

Reviewed the logs, couldn't get much information.

AUTO_MAIL_INTERVAL is 2

Please advise what might be causing this issue

Appreciate your help