When adding recepiants, click the + sign. And if you need to add more users you need to click the +, Pick InfoBurst user, pick and add for each additional user. It takes 7 clicks to add each user. Adding 10 users = 70 clicks.
When the user list comes up enable the ability to use the CTRL or SHIFT key. CTRL = Many one at a time, SHIFT = Pick a range of user. Click SAVE to add them