The destination domains do not accept mail from the source SMTP server is the reason for a 554. This can be many things, in rctp to a wrong addressee up to the issue that e.g. the destination system can not determine the A-record of the source or this is wrong.

Off the top of my head: Is the sender IP or sender domain on a blacklist? https://mxtoolbox.com check your own mail server here

George

to follow-up on this: mxtoolbox shows passing for all tests today. Error still exists.
No Blacklist. DKIM, DMARC and SPF all passing.

Just to confirm: no others using SMG are having issues sending mail to icloud.com, me.com and/or mac.com domains where the gwia is using SMG as the outbound relay?

I have the same configuration but no mail address to test ... 

Hot off the press. Give this a shot Diethmar Rimser 

groupwisemedic@icloud.com

This is a throwaway email account from my burner iPhone. If you get a bounce or get thru please let me know. 

Seemed to go thru ...

The mail is delivered without any problems from my GroupWise system

Something else is faulty here. Check here to see if the mail you are sending has a bad rating. https://www.mail-tester.com/?lang=en

SMTP 554 definitely indicates that smtp target does not recognize the mail address. It is also possible that the user is disabled. 554 is actually a hard bounce

Check that your iPhone is using the "internal" WLAN behind your firewall and run a trace for sending mail. See what happens then. The error is on the sender side

Thanks all and Georg H. Weber  and Diethmar Rimser . I think I found the issue. 

It may be how the Apple domains accept email due to a new change in their environment (or it's my environment?). Again this issue started the week of January 15th. I have been using the same setup to attach my Privacy Policy via SMG for at least 2+ years without issue.

The issue appears to related to the Outbound Mail Filter Policy and the Message Signature thingamabob. In my environment, when the Message Signature banner is connected to the Message Outgoing thingamabob mail fails to Apple domains. Disconnect the Message Signature banner and mail is delivered - no problem.

Perhaps, someone can confirm this by sending an email to groupwisemedic@icloud.com and let me know if your mail bounces with Message Signature connected as shown below.

At this point in need to find a new process to attached our confidentiality statement (we use Global Signatures in GW for another purpose). 

Thanks