Workflow emails

Hello,

I have created a field known as the "Next Follow Up" field in the four main entities COLA. I have also created a workflow for each entity that Waits 7 hours after the date shown in Next Follow Up (7am) and sends an email to that user as a reminder. The emails are only sent if the user logs into Outlook through a PC. Since all of our salesforce are using iPads, they do not receive the emails. How can I fix this?

Thank you for the help!