Repeated Temporary Recipient Failure for BCC Address

Hi everyone! I have been sending out multiple emails where I bcc-ed the Hubspot bcc email address but for all but one of them, I have been getting “Temporary Recipient Failure” with the administrator diagnostic information shown in the screenshot below. Given the error message, I thought it might just be temporary, but even after a few tries at a later time the issue still persists. My connected email account is also far from reaching the daily rate limit of emails. Could anyone please advise on what I can do to fix this issue? Thank you!