The recipient list for campaigns is only created when the campaign is scheduled to go out. This allows you to dynamically update campaigns without having to re-run the report you used to create the campaign.
For example: If you create a report on a Monday afternoon to be sent as a campaign on a Wednesday morning, but on Tuesday you change a patient's email address or add more patients to your patient list, then these updates will be automatically applied to the campaign when it is sent on Wednesday.
The next time that you set a campaign and see that it has no recipients, check when the campaign is scheduled to be sent. If it is scheduled to be sent at a later time or date, then the list of recipients will be generated at the scheduled time (the recipient list will grow dynamically as messages are sent by our mail server). If the campaign has already been sent and has fewer recipients than you expected, contact us at firstname.lastname@example.org to look into it further for you.
You can see when the campaign is scheduled to be sent out by running a communication report with the type set to Campaign. Campaigns that you have scheduled to run in the future will have a status of "Scheduled" in the campaign report list.
The time that the campaign is scheduled to go out will appear in the "Sent" column of the campaign report list.
If you would like to change the time/date of the scheduled report, you will need to cancel the campaign and reset the campaign from the report list.