Based on the error message you are receiving '550 High probability of spam', it looks like the email bounce is originating from something on your end rather than the recipient's end. It seems like you may have certain security filters set up in your email that are scanning the emails you send to detect any potential spam and prevent any potential spam emails from sending out to your recipients.
Therefore, the best next steps to resolve would be to contact your own email administrator to flag the bounce here and check for any spam/security software on your side flagging the contents of the email.
If you still having this issue after you have checked this with your team please let me know
Thanks
Sharon
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