Here is something you could do for clients as part of your services:
Simple Direct Mailing using Gmail
In G+ & Gmail, perhaps using Rapportive, circle each strong contact made;
Use both niche and generic circles to provide a unique profile;
Select Contacts in Google Gmail;
Now select the top level Circles;
Add key contacts from the displayed list to a new circle, eg Mailing List;
Once complete, select the new circle Mailing List;
Click on the Google Groups button;
In your Gmail Compose, enter Mailing List in the Bcc option;
To add new contacts, revisit Circles, select contacts, click Google Groups
Voila – Simple Direct Mailing using Gmail