Hello @PDCollabAdmin ,
I'd recommend looking at our main article on managing bounces, so you can know what your best path forward is based on the bounce type we're given for the contact in the reporting.
You may also want to have the contact look into safelisting your address just for additional deliverability padding on their end. If you continue to have issues with this particular contact, you may want to call our Delivery team for some additional insight / advice.
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