Hello @Joanne_M ,
A contact becomes suspended in our system when you or other customers of ours have tried to send to them in the past, and they've bounced back from the domain / IP as non-existent. Make sure to check out our main article on suspended bounces for additional insight. If we receive a report from their domain / ISP about them being 'non-existent' again, then they'll be put back into suspension.
If the non-existent / suspended bounce occurs again for the viable contact, then it may be worth reaching out to our Delivery team to see if they have any additional insight regarding that domain / ISP. Otherwise, there's not much else that can be done in this regard, if their ISP either doesn't recognize their address or refuses to deliver the email.
Suspended Contacts FAQ
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