Update - The only communication we've had from the other parties is that the previous advice holds true and that good mail sent from our clean mail IP addresses from domain's with a correctly formatted spf record should result in the mail being received correctly by mailboxes they provide. Communication is slow but ongoing and we're pushing as hard as we can for a definite resolution of this issue.
Jan 7, 16:42 GMT

Update - We are still seeing some rejections and delayed messages to these mail providers and are continuing to work to resolve these problems. We apologise for the ongoing nature of this issue and for the inconvenience caused.
Apr 13, 14:20 BST

Identified - We are seeing that a number of rejections to BT and Yahoo are being caused by badly formed SPF records. If you are having issues sending to addresses with BT and Yahoo from our systems we recommend using the following SPF:-

v=spf1 exists:%{i}.mta.spf.extendcp.co.uk exists:%{i}.web.spf.extendcp.co.uk -all

If you need any assistance in updating this our support team will be happy to help.
Feb 10, 17:52 GMT

Investigating - We are seeing some failures as well as delays with Mail Delivery to BT and Yahoo addresses from messages sent from our network.

Our System Administrators are currently working on this and we will provide further updates here as we have them.

We apologise for the inconvenience caused as a result of this
Jan 23, 12:30 GMT

Investigating - We are seeing that a number of rejections to AOL, this looks to be caused by a limit on their servers restricting the amount of emails that can be received from our shared mailservers. We are currently investigating, our apologies for any inconvenience caused here in the meantime.
Apr 6, 13:04 BST

Monitoring - This is still ongoing, we are continuously monitoring this and will keep this page up to date with the latest information.
Nov 28, 14:21 GMT

Investigating - We are currently seeing a large amount of emails being deferred when sending to hotmail/outlook and other microsoft addresses. This includes and domains that have emails hosted with outlook services.

This looks to be caused by a limit on their servers restricting the amount of emails that can be received from our shared mailservers. Our admin team is currently investigating and attempting to contact them for further details, or a possible work around.

On inspection this may not be effecting all emails sent to these addresses, but a large amount are being blocked. This will cause bouncebacks to the sender, so you can see which emails have been blocked.

Our apologies for any inconvenience caused here in the meantime.
Oct 21, 15:45 BST