Mail blocked ERR 554 5.1.8, accidentally sent to the same email address twice while sending out cold emails.

Mail blocked ERR 554 5.1.8, accidentally sent to the same email address twice while sending out cold emails.

My mail account got blocked because I sent out the same email to one account twice while sending cold emails. I send all the mail one by one so it's not spamming, but I can be sending out the mail too quickly.