Timedifference between Triggering alert and notification


I am using Grafana v5.4.3 on a CentOS server. As datasources i use InfluxdBs.
I have the following problem: I set alerting rules for several channels. These rules include the “for xmin” option. So grafana has to check the alert for example 60min before changing the state to alerting. This part works perfectly fine. The problem appears with the notification. I get the mail one hour after the alert was triggered. Does anybody know why that happens or where I might have made a mistake in the config?
Thanks for the help!