Incoming email bounced

[#1]

Hi,
I've had several incoming emails bounced back to their sender today. The mailbox is set to redirect to a gmail account. It's happening with some mail sent from at least two different accounts (one gmail, one a corporate account), but sometimes it gets through.
I have disabled plusnet spam filtering on that mailbox. Is that likely to fix the problem, or could it be a problem with cloudmark?
Shall I post the Failure notification here? It says:
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 552 552 Spam Message Rejected  (state 17).
Thanks,
Paul

[#2]

Hi there,
Just to clarify, are you saying that messages to one of your Plusnet addresses that then in turn redirects to a googlemail address (I can see one of your mailboxes is set up to do that) is being bounced by google?
If that is the case it would suggest from

Quote

Google tried to deliver your message, but it was rejected by the recipient domain

that your gmail is trying to forward that message on somewhere else again which shouldn't be the case really.