Outgoing emails are not sending from one particular site, "immediate alerts" timer job stuck on some specific database, owstimer.exe consumes high memory on one SharePoint server.
You can restart SharePoint timer service (SPTimerV4), but after some time the same happens again. If you have courage to wait enough - you can see 100% CPU load and WFE server not responding.
In my case it was an incorrectly designed custom workflow which generated hundreds alerts per minute,
so "Immediate Alerts" timer job just was not able to process them.
The solution is very simple. After you track the problem down to the site - move all sites out of content database and dismount that database.