Storyline's platform is built on the same real time delivery infrastructure used by Fortune 100 companies but there are a few reasons why some contacts may look like they should be receiving messages but aren't:

• There might be a timer or delayed send on the message: Storyline allows you to delay sending a session - both at your account level and on individual programs. In this case the message will be held until the sending window opens.
• The phone number or email may not be correct: It's possible that the phone number or email associated with that contact is incorrect or out of date.
• They may have blocked you: Don't spam people or they will block you, and that can cause all sorts of problems. Make sure that you're following Storyline's best practices.

Follow Storyline's best practices to ensure maximum deliverability and acceptance.