To print a single #10 business envelope:
Open the Client or Contact's profile and right-click on the address that you wish to use. Select "Envelope" from the menu that appears.
To print a #10 business envelope for each member of a group:
Open the Group's profile and select "Mail - Envelopes" in the Reports section on the left side of the screen.
To print envelopes of a custom size:
Create a Word Envelope template using Merge to Word and Microsoft Word's Mail Merge tool.
For details on all of these tips, as well as setting up your envelope printer, press F1 to open Help, and search for Envelopes on the Index tab.