Office365 and a new IP address

Wondering if anyone on the list has ever set up a mail filtering appliance or server on new IP address and had to deal with 451 messages from Office 365.

We're processing a large volume of mail and seem to be throttled by O365. Seeing something like this:
451 4.7.500 Server busy. Please try again later from [x.x.x.x]. (AS77713180) [ ].

We own the IP block and the address itself is not on any block lists.

It's been going on for a few days now, pissing off a lot of our customers. As expected O365's front line support is totally useless.

Any advice would be appreciated!


Are you properly rate limiting and warming up the new IPs sending volumes
or just sending at normal speeds?

Are you properly authenticating your email with SPF, DKIM and SPF as per
the Postmaster page suggestions for sending email?

Are you properly enrolled in SNDS, Junk Mail Reporting etc...

More self help tips and how to contact MSFT for support can be found here:



No, unfortunately my appliance doesn’t have a method for rate limiting. I’ve had to replace my old appliance and move it to a new IP.
My incoming volume of mail to be filtered is far higher than the throttle anyway.

For the most part my customer domains have SPF records that point to my outgoing hostname.

Yep, enrolled in all those.
However it seems the suggestions on site only apply to and not Office 365 tenants.

What it boils down to is I’m looking for a method to speed up this IP reputation throttling.

I appreciate the suggestions.