I have an office 365 developer tenancy. I wanted to try the option of Email alerts through the Mail enabled Security groups.
I have created a new Mail-enabled security group(AlertTest) and added few users to the group. My site structure has unique permissions at all levels.
So I have added the "AlertTest" group to SharePoint Security groups which have read access at the Site collection level, subsite level and also at the library level.
And then created an alert for the "AlertTest" group on the library. But it didn't send out the even the subscription notification to the members of the group