Outbound mail blocked

[#1]

We are getting repeated error 452s on outbound mail when sent  by desktop clients via authenticated SMTP from non-PN IP addresses  -  one site in particular (we have a  business account and work from several customer sites).  Some have individual addressees and some are ‘bulk’. None have more than 100 addressees and we are nowhere near the 1000 addressees per hour limit. The content of all is innocuous: a few lines of anodyne text and no URLs.  I raised ticket #75163408 on 30th Sept but am no nearer a solution or a workaround. I assume my non-PN sites are being continually greylisted by the 'outbound' Cloudmarks but have no idea why. Any help (Bob P?) appreciated.

[#2]

The outbound policies are more aggressive off network. I'll take a look at your ticket when I get to the office...

[#3]

Tnx Bob.
Since you may wish to keep Cloudmark's more detailed settings private, feel free to reply on ticket rather than on board.

[#4]

Could do with a bit more info. I've just bounced the ticket back to you.

[#5]

Ticket #75163408 now updated with the detail requested.

[#6]

Thanks, nudge me tomorrow if you've still not heard anything.

[#7]

This post has been also discussed off-board by ticket.
I though it worth summarizing the outcome for the benefit of others who have a similar problem. As is a usual request from most email service providers, open publication of anti-spam detail (i.e.  Cloudmark settings) has been withheld.
Those sending email via PN’s SMTP servers via the Cloudmark traffic filters from non-PN addresses (i.e. from another ISP) have a limit of ‘total number of addressees per time period’ which is smaller than that imposed on those sending from PN IP addresses. The reason is obvious and understandable. My eventual workaround has been to move bulk email to an external SMTP service. We chose Mandrill because PN hosts many of our domain names and, unlike other large providers, Mandrill do not impose a charge per domain name (unless the customer wants a unique IP address per domain name) but only on the aggregate number of addressees. The downside of using an external SMTP service with mail sent from a PN-hosted domain is that – to the recipient – the sender is not ‘whitelabel’, i.e. the sender is shown as (e.g.) fred@smtp_service_supplier.com on behalf of fred@eagle.com. Whitelabelling (showing the sender as just fred@eagle.com) needs DKIM and SPF information added as TXT records to the PN hosted domains (this is to give added credence that the email is really being send from those domains), but unfortunately user-defined TXT records are not supported by PN. To prevent the non-whitelabel sender name appearing too cryptic to the recipient, we registered and hosted elsewhere a domain name which the recipients would understand (i.e. the name was in the same 'type of business' as the PN domain names themselves) and added SPF and DKIM TXT records to it. The result is that the recipient  sees  (e.g.) fred@bird-mail.com on behalf of fred@eagle.com