Check your SPF, DKIM, and DMARC records
SPF, DKIM, and DMARC are the three security mechanisms that protect you from hackers, phishers, and help to avoid spam. ISPs treat these seriously, so before you start using your new email account for campaign sending, you need to set them up.
Learn how to set up SPF record here
Read how to set up DKIM here
Read how to set up DMARC here