Warning in Postfix maillog file may appear as the following:
Aug 1 15:36:45 imsva235 postfix/cleanup: A024B1A03B: warning: header X-IMSS-TLS-USAGE: Used from unknown[10.64.1.1]; from=<email@example.com> to=<firstname.lastname@example.org> proto=ESMTP helo=<test>: Used TLS for UNKNOWN
Aug 1 15:32:25 imsva235 postfix/smtpd: warning: proxy inet:127.0.0.1:10020 rejected "RCPT TO: <email@example.com>": "421 Service not available,closing transmission channel"
This is normal message, and there is no need to be alarmed about it.
In the first message, Postfix 2.8 displays an information instead of a warning. IMSVA 9.1 uses Postfix 2.7.1, so that it contains this information. In future versions, IMSVA will upgrade Postfix version to enhance this.
In the second message, FoxProxy module rejected the mail, causing Postfix to this warning. This is an expected result.