DNS Blacklist Help?

[Megan 0]

We have a customer located in Taiwan that cannot e-mail to our sales rep. The customer gets this error:

The original message was received at Wed, 27 Feb 2019 14:08:59 +0800

----- The following addresses had permanent fatal errors -----

----- Transcript of session follows -----

... while talking to asp.reflexion.net

>>> RCPT To:<removed email>

<<< 553 Your IP [202.39.18.43] is on one or more DNS blacklists. ulc: 9223357036843801172, rcp: 0001. (#5.1.1)

I'm not sure how to go about troubleshooting this?