I've been trying off and on for years to get email alerts in my Outlook email when people post questions and other activity in the Mentor Communities. This is what my basic settings look like:
I went through all the options I could find again today and found one that might help, we'll see... the language and locale settings... mine were blank. I changed them to english and United States and maybe that will help. If you've had similar experience and solved it let me know so I can try that too!
If customers are having the same difficulty it might give them the impression of lack of activity in the communities and might limit responses they could potentially get to only those people who proactively log in every day or so to check for activity... (not likely a habit most people would be keen to keep up when only one post a week is happening to begin with)