Check if your IP address is listed in DNSBL (also known as RBL). This tool checks your IP against 76 DNSBL database by simple one click.
A DNS-based Blackhole List or Real-time Blackhole List is a list of IP addresses which are most often used to publish the addresses of computers or networks linked to spamming; most mail server software can be configured to reject or flag messages which have been sent from a site listed on one or more such lists.
— Source Wikipedia