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In order to add an individual to just one card, you would have to add them to the board.
It's not possible to add someone to a card without adding them to the board.
I know that's not what you want to hear, but unfortunately, it can't be done.
Feel free to come back with further questions, that's what we're here for!
Unfortunately you cannot do this. However, you can use Hipprello for this purpose. Hipporello enables you to build form and lets your customer create Trello cards through these forms. After defining your forms like contact us, feedback, bug report, etc, forms will be displayed in a service desk portal. When your customers fill the form, a Trello card will be created for each request. Your customer will only see what they submit and further communication log on Trello card.
Besides this, you can forward your emails like sales@, support@, hr@, etc to Hipporello's email to board addresses. For each received email a Trello card will be opened. In this way, there will be a central communication center that all incoming requests are converted to a Trello card.
Hipporello has many features. Please check out our website and Trello power-up page for this:
Hello Community! My name is Brittany Joiner and I am a Trello enthusiast and Atlassian Community Leader. I'll be sharing with you a series of videos with my top tips on how to best use Trello...
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