Alert Email Delay

Hi,

I have a 90D running 5.2.9.  We have had email alerts set up for a while for anything "Critical" and above, and it mostly works fine.  The one issue I have is that there is a delay, sometimes of several hours, between an event and the alert email.  If I configure for specific events there is an Interval option, but no choice with the level-threshold option.  Can't seem to find anything in CLI guides that address this either.  Has anyone found this and/or fixed it?

thanks