Email deliverability - Installing SPAMASSASSIN or similar to reduce SPAM

I have a LAMP Server from Contabo. I do NOT send mass or bulk emails. My Server got listed under UCEPROTECTL3. With that my outgoing emails are bouncing back.

I need help on the following:

1. Install SPAM removing software on LAMP server (SPAMASSASSIN or alike)
2. If possible to get removed from UCEPROTECTL3