Two of my clients have problems with zoho mail service. Any solution yet?

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ERROR_CODE :554, ERROR_CODE :5.7.1 <END-OF-MESSAGE>: End-of-data rejected: Blocked using 2 dnsbls, INFO: "http://www.lashback.com/support/UBLLookup.aspx?IP=74.201.84.163" "IP 74.201.84.163 is UCEPROTECT-Level 1 listed. See http://www.uceprotect.net/rblcheck.php?ipr=74.201.84.163"

and

The mail system

host mx.zoho.com[165.254.167.50] said: 541
5.4.1
    Mail rejected by destination domain (in reply to RCPT TO command)