Problems delivering email to icloud email accounts

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: [17.172.34.9].




Diagnostic information for administrators:
Generating server: mail.mycompany.com
email@icloud.com
[17.172.34.9] #<[17.172.34.9] #5.0.0 smtp; 5.1.0 - Unknown address error 550-'5.7.0 Blocked - see https://support.proofpoint.com/dnsbl-lookup.cgi?ip=96.56.26.14' (delivery attempts: 0)> #SMTP#


I checked with proofpoint and our server is not blocked
primetime24Asked:
Who is Participating?
 
timgreen7077Exchange EngineerCommented:
if it happens on any iCloud account and it seems proofpoint is your smarthost, you may need to contact them and inform them of that.

before doing that send a test email to your iCloud account from gmail or something and see if successful. if it fails that also then there may be a issue with iCloud accounts or something at the moment, but if successful, contact proofpoint and inform them.
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timgreen7077Exchange EngineerCommented:
the error indicates that the address is unknown. verify the email address is a accurate and misspelled or anything
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primetime24Author Commented:
I've tried with my personal icloud email address and have gotten the same results
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primetime24Author Commented:
It's not exclusive to any one icloud email address, It's any email address affiliated with icloud
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timgreen7077Exchange EngineerCommented:
Recommended author looks at proofpoint support for solution, since only icloud accounts are affected. closing ticket unless author reopens requiring further assistance.
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