SCOM service alerts not being sent to Distribution list

Hi Team,

We have configured service monitoring for a particular server. I would like to know why alerts are not being sent to DL's configured but the same has been triggered to the individual ID. Which configurations has to be checked. This happens recently and in most of the configurations. Application teams keeps complaining that they are not receiving alerts. 

Please see the below link for more details. I was not able to fix it further.  

https://social.technet.microsoft.com/Forums/systemcenter/en-US/1ecada58-0d42-4acf-8a63-44df12e12102/scom-service-alerts-not-being-sent-to-distribution-list?forum=operationsmanagermgmtpacks