I have been trying to get this resolved thru DH support, but no luck so far.
We route our MX records to an external filtering service "PUREmail" (similar to Postini). They block spam/ virus, and deliver clean email to DH mail-server (mail.mydomain.com).
Therefore, ALL our incoming email appears to come from same IP addresses belonging to PUREmail. However, DH mail-server thinks that PUREmail is sending excesive email to them. As such, DH is rejecting with "SENDER_QUOTA_REJECTION".
I believe DH does not block/throttle email delivered by Postini. How would I get them to do the same thing for PUREmail. I suspect many new DH customers might be using PUREmail (they are actually better than Postini in terms of filtering accuracy).
In fact, DH shold welcome such arrangements where spam/virus is already blocked outside DH networks. And, all the email reaching DH servers is guaranteed to be CLEAN!
Here is the entire bounce message (I have replaced actual email address with email@example.com):
rejected RCPT firstname.lastname@example.org: response to "RCPT TO:email@example.com" from mail.mydomain.com [22.214.171.124] was: 554 firstname.lastname@example.org: Recipient address rejected: Policy Rejection: --SENDER_QUOTA_REJECTION--