I'm trying to send email from my corporate exchange email server to iCloud email addresses and it comes back undeliverable. the error is as follows
A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.
The following organization rejected your message: [188.8.131.52].
Diagnostic information for administrators:
Generating server: mail.mycompany.com
[184.108.40.206] #<[220.127.116.11] #5.0.0 smtp; 5.1.0 - Unknown address error 550-'5.7.0 Blocked - see https://support.proofpoint.com/dnsbl-lookup.cgi?ip=18.104.22.168'
(delivery attempts: 0)> #SMTP#
I checked with proofpoint and our server is not blocked