Checking/monitoring your server IP(s) against RBL(Real-time Blackhole List) lists is always a good thing to do. You can go on sites like spamcop.net, abuseat.org etc and check for your IP or you can use a service that will check your IP against many RBL lists. Such a service is https://mxtoolbox.com/blacklists.aspx which will check your IP on 100+ RBL lists.
As of March 2021, the RBLs are:
0SPAM
Abuse.ro
Abusix Mail Intelligence Blacklist
Abusix Mail Intelligence Domain Blacklist
Abusix Mail Intelligence Exploit list
Anonmails DNSBL
AntiCaptcha.NET IPv6
BACKSCATTERER
BARRACUDA
BLOCKLIST.DE
CALIVENT
CASA CBL
CBL
CYMRU BOGONS
CYMRU BOGONS IPv6
DAN TOR
DAN TOREXIT
DNS SERVICIOS
DRMX
DRONE BL
FABELSOURCES
HIL
HIL2
Hostkarma Black
IBM DNS Blacklist
ICMFORBIDDEN
IMP SPAM
IMP WORM
INTERSERVER
ivmSIP
ivmSIP24
JIPPG
KEMPTBL
KISA
Konstant
LASHBACK
LNSGBLOCK
LNSGBULK
LNSGMULTI
LNSGOR
LNSGSRC
MADAVI
MailBlacklist
MAILSPIKE BL
MAILSPIKE Z
MSRBL Phishing
MSRBL Spam
NETHERRELAYS
NETHERUNSURE
NIXSPAM
Nordspam BL
Nordspam DBL
NoSolicitado
ORVEDB
PSBL
RATS Dyna
RATS NoPtr
RATS Spam
RBL JP
RSBL
s5h.net IPv6
SCHULTE
SEM BACKSCATTER
SEM BLACK
Sender Score Reputation Network
SERVICESNET
SORBS BLOCK
SORBS DUHL
SORBS HTTP
SORBS MISC
SORBS NEW
SORBS SMTP
SORBS SOCKS
SORBS SPAM
SORBS WEB
SORBS ZOMBIE
Spam Eating Monkey SEM IPv6BL
SPAMCOP
Spamhaus ZEN
SPFBL DNSBL
Suomispam Reputation
SWINOG
TRIUMF
TRUNCATE
UCEPROTECTL1
UCEPROTECTL2
UCEPROTECTL3
Woodys SMTP Blacklist
Woodys SMTP Blacklist IPv6
WPBL
ZapBLOn that site, you can create an account and create monitors for your IPs. The free plan includes one monitor and it is free.