I really wanted to move all of my "important stuff" to Fastmail but I found the emails I was sending kept getting caught in spam mail of the receivers, especial

I really wanted to move all of my "important stuff" to Fastmail but I found the emails I was sending kept getting caught in spam mail of the receivers, especially to Outlook emails. This is using the default fastmail.com domain I know it's not Fastmail's fault but it's a big dealbreaker for me since a lot of professional emails are on Gmail / Outlook. I had this same issue with Proton, missed some opportunities because they didn't even see my mail.