My outgoing emails are being blocked by the postmaster of my ISP as spam.

My outgoing emails are being blocked as spam by my ISP postmaster. I was directed to the spamhaus site to delete the IP address. After doing so, I was able to send mail for a few days before problem returned. Only happens on the MacBook. Android, iPhone and PC not having same problem using same email address and ISP. Was told by my ISP to contact Apple support.

[Personal Information Edited by Moderator]