Can Gmail or Outlook users add more than one recipient in a campaign?
Currently, there is no ability to add the same email address onto more than one campaign at a time. If you would like to include a user on another campaign, you will need to manually remove them from the current campaign they are on, and move them to the new, desired campaign.
Manually move a recipient to a new campaign
Click into the campaign > "Recipients" tab > check the box next to their email address > 'Move To' button at the top of the page and select the new campaign.