Since we migrate on Zimbra we got sometime mails refused in error 550 5.7.1 as:

<>: host[] said: 550 5.7.1 Your email
messages have been blocked by the recipient OR by Trend Micro Email
Reputation Service. Contact the recipient or his/her administrator using
alternate means to resolve the issue. (in reply to RCPT TO command)
These addresses had no problems before, have you an explication ?

Thanks in advance.