Every IP has IP reputation.
IP address is given a low or negative reputation when they are found to be sending high numbers of spam emails.
IP address is given a high or positive reputation when they are sending legit emails.
When the IP's reputation will go low and that will affect email deliverability as you are using the same IP address. The email could land on Junk folder or be rejected until the IP's reputation return to high state.
There are a lot tool provide IP reputation checking as below.
1. MxToolbox ( https://mxtoolbox.com/blacklists.aspx )
2. Talos ( https://talosintelligence.com/ )
It will show you if the reputation of your domain or IP is judged as Good/Neutral/Poor. Good means nothing to worry. Neutral means there is area of improvement, Poor means that most of your emails might not be going into the inbox.
3. BarracudaCentral ( https://www.barracudacentral.org/lookups )
4. MailTester ( https://www.mail-tester.com/ )
Mail-tester will analyze your message, your mail server, your sending IP. and show you a detailed report of what's configured properly and what's not.
If the IP reputation is bad, do carry out checking on the email queue.
For cPanel server, refer https://support.exabytes.com.my/en/support/solutions/articles/14000127947-mail-queue-manager for the guide.
For Plesk server, refer https://support.exabytes.com.my/en/support/solutions/articles/14000128148-how-to-view-mail-queue-in-plesk-linux for the guide.
If you need an assistance in analyzing the email delivery activity, please engage with technical support team for custom technical charge assistance.