Outbound email being quarantined for Office 365 customers

Proofpoint have identified an issue where some customers on O365 are having their outbound email quarantined in error, the email below details this and describes a remedy. If you have customers impacted by this then the short term fix is to stop routing outbound via Proofpoint.

Please make sure that all customers sending outbound via Proofpoint have the Sending Server IP's configured.

These emails have been sent from numerous O365 IP addresses, however the IP's are not listed as sending servers in the user interface.

As part of our last release, more checks were introduced to confirm that any emails sent outbound have the correct sending IP listed under their account.

Engineering are currently reviewing this behaviour as there is no bounce back generated. Here is the list of CIDR blocks that need to be added to the customers sending server IP list.

23.103.132.0/24
23.103.133.0/24
23.103.134.0/24
23.103.135.0/24
23.103.144.0/24
23.103.145.0/24
23.103.146.0/24
23.103.147.0/24
23.103.191.0/24
23.103.198.0/24
23.103.199.0/24
23.103.200.0/24
23.103.201.0/24
23.103.202.0/24
23.103.203.0/24
23.103.204.0/24
23.103.205.0/24
23.103.206.0/24
23.103.207.0/24
23.103.136.0/24
23.103.137.0/24
23.103.138.0/24
23.103.139.0/24
23.103.140.0/24
23.103.141.0/24
23.103.142.0/24
23.103.143.0/24
64.4.22.64/26
65.55.83.128/27
65.55.88.0/24
65.55.169.0/24
94.245.120.64/26
134.170.132.0/24
134.170.140.0/24
134.170.171.0/24
157.55.133.160/27
157.55.158.0/24
157.55.159.0/24
157.55.206.0/24
157.55.207.0/24
157.55.234.0/24
157.56.73.0/24
157.56.87.192/26
157.56.108.0/24
157.56.110.0/24
157.56.111.0/24
157.56.112.0/24
157.56.206.0/24
157.56.208.0/24
157.56.209.0/24
157.56.210.0/24
157.56.211.0/24
207.46.51.64/26
207.46.100.0/24
207.46.101.128/26
207.46.163.0/24
213.199.154.0/24
213.199.180.128/26
216.32.180.0/24
216.32.181.0/24

There maybe additional IP addresses not listed above.

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