This has been a persistent problem but I am just now trying to tackle it.
Previously the error seemed to only localized to our domain
Note: we have a primary and a backup mail server, such that all inbox mail is forwarded to email@example.com
Where the sender is mail.company
Apr 20 10:12:04 zimbra-mta postfix/smtp: A587E804003: to=<firstname.lastname@example.org>, relay=backupmail.company.com:25, delay=0.
09, delays=0.05/0.03/0.01/0, dsn=5.4.6, status=bounced (mail for backupmail.company.com loops back to myself)
Now I am starting to see this error for domains other than my own.
Apr 20 08:42:31 mta postfix/smtp: 5B3BB804003: to=<email@example.com>, relay=nk11b01-smtp-mx002.me.com[22.214.171.124]:25, delay=0.13, delays=0.05/0.02
/0.06/0, dsn=5.4.6, status=bounced (mail for me.com loops back to myself)
Apr 20 08:09:31 mta postfix/smtp: 827A1804001: to=<firstname.lastname@example.org>, orig_to=<email@example.com>, relay=mail1.supportcentero
nline.com[126.96.36.199]:25, delay=0.09, delays=0.05/0.01/0.04/0, dsn=5.4.6, status=bounced (mail for supportcenteronline.com loops back to myself)
Im not really sure where the issue lies however the first error i think is on the backupmail server.