Adobe Campaign Classic
In 9032 of Campaign, when a delivery attempts to compile and send to some recipients, and if HTML content errors like the one below are hit:
then the recipient is flagged as unreachable and quarantined.
Currently there isn’t a way around this issue, other than the workaround to pull the recipients out of quarantine and attempt to resend a delivery.
NEO-23161 has been opened and being investigated by Adobe R&D for a permanent fix in a future release.