Under ZCS 7.0.1 network I'm seeing an issue with 3rd party email clients smtp connections on slower networks and file attachments. There seems to be a timeout set to around two minutes on SMTP connections. I'm seeing the following error in the logs and on email clients when it takes over two minutes to send an email.

Mar 29 10:16:38 email postfix/cleanup[21031]: 6391C3536001: milter-reject: END-OF-MESSAGE from ip72-220-140-199.sd.sd.cox.net[]: 4.7.1 Service unavailable - try again later; from=<millerdc@domain.com> to=<doej@domain.com> proto=ESMTP helo=<[]>
Mar 29 10:16:38 email postfix/smtpd[18443]: disconnect from ip72-220-140-199.sd.sd.cox.net[]

Now I have tested this on multiple speed connections and have ruled out that it is the size of attachment and email client. For example at home I get around 250K/sec to my work zimbra server. So I can send about a 15MB attachment with out getting the error. Anything longer goes past the timeout. From a faster net connection that gets about 2MB/sec I can send a 150MB attachment. What do I have to change to increase the timeout on smtp connections? Thanks.