System I/O error (in reply to end of DATA command) for LMTP delivery

I'm receiving a 451 4.3.0 System I/O error (in reply to end of DATA
command) error from Postfix when trying to deliver to cyrus-imap and not
really sure why. I'm on CentOS 7 (2.4.17-8) after downgrading from current
version. I'm using Kerberos GSSAPI to connect to the front end, but
authentication appears to be working fine as I can see authenticated when
enabling LMTP debugging in Postifx. All messages are refused for delivery
though. I'm not sure what to do. Any suggestions?

Steve

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