大家看下这个退信什么意思?要如何处理

dxjabc

did not reach the following recipient(s):
paulaliuqd on Fri, 20 Oct 2006 10:31:31 +0800
    A critical function required for the transfer or delivery of the message was not supported by the originator of the report
    <****.*****.local #5.3.3 smtp;500 5.3.3 Unrecognized
command>