Issue with emails that I send being rejected by Outlook's postmaster - no fixes work

This has been going on for a year now. Whenever I use my email account to reply to an email, Microsoft's Postmaster rejects it as spam.
The only way I can "reply" to emails is to forward that email to another email address that I use (a separate account) and reply to it from there.

I have tried numerous times to fix the issue, and none of the methods worked (especially after spending many hours chatting with tech support).

I am losing my patience with Microsoft over the matter.