I understand you're looking at automatic alerts when a new user registers in your community. Unfortunately, I don't see that this is available unless moderation is enabled (and you are the moderator) or potentially through customizations. You may also potentially report against registered users using either CMR or Data Export Service (latter option may require some development work), but this won't be automated alerts in that sense.
On your second question, could you please clarify what you mean by 'Welcome Email' policy? And what are you intentions or use case details?