delivery-notification FAILED: temporarily unable to send DSN

[Danny Roberts via amavis-users]

I am using a combination of OpenSMTPD/Dovecot/Amavisd(Clamd/Spamassassin) for 
a mail server.

I am seeing a lot of the following messages in the maillog:

May 14 11:49:50 mail smtpd[22409]: relay: TempFail for d5b0bef3e46ade55: 
session=f8402c9c9b9ce396, from=<newelskkg4 at remingtonseeds.com>, 
to=<simoe at lindhurst.co.uk>, rcpt=<->, source=127.0.0.1, relay=127.0.0.1 
(localhost), delay=1h1s, stat=451 4.5.0 Error in processing, id=22378-01-2, 
delivery-notification FAILED: temporarily unable to send DSN to 
<newelskkg4 at remingtonseeds.com>: 451 4.5.0 From MTA(smtp:[127.0.0.1]:10025) 
during fwd-rcpt-to (No response to RCPT (<newelskkg4 at remingtonseeds.com>), dt: 
0.000 s): id=22378-01-2 at /usr/sbin/amavisd line 13807.

The only similar things I've seen online are someone having issues with Postfix 
and custom Java code.

Telnet to that port shows the following:

[root at mail conf.d]# telnet 127.0.0.1 10025
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 mail.lindhurst.co.uk ESMTP OpenSMTPD
^]
telnet> quit
Connection closed.

Regards,

Danny Roberts
www.thefallenphoenix.net