What does "550 Rejected by content scanner (CMAE)" mean?
When the CMAE service rejects mail due to bad content, it is only because it positively recognized, this recognition is based on human signature analysis using the CMAE system.
The CMAE pre-filter is sensitive to the content of your mail and will reject your email if it contains the fingerprint of spam content.
Ensure your email does not have 'spammy' content such as references to medications or low cost jewellery etc.
Avoid forwarding email from senders that may have been badly classified, as their email footer may be enough to identify the email as coming from a known spam source.
If your email is rejected because it is a forwarded email from a bad sender, try copying the relevant content into a fresh email and perhaps send as 'plain text'.
Certain URL's (web links) have been classified as inappropriate or have been used by spammers. If your email contains these, and you are sure you want to send them, you should obfuscate the address to avoid it being recognized by the filter.
Since the introduction of the CMAE filter, individual users have been able to submit feedback about spam that may have slipped through the net or genuine mails that have been blocked by the CMAE Filters (ham). This re-active reporting, benefits the CMAE filter system as a whole, but only if feedback is sent to the CMAE system in the correct format.
A false positive is a legitimate message that the CMAE filter has incorrectly classified as spam or phishing.
A false negative is a spam or phishing message that the CMAE filter has incorrectly classified as legitimate.
The CMAE filter’s accuracy depends on feedback from end users. By reporting incorrectly-classified messages promptly, you contribute to the accuracy of the CMAE filer service.
The messages that you report must be in RFC822 format as MIME attachments. This preserves the email header information that the CMAE feedback system requires.
False negatives should be forwarded as an attachment (containing up to 10 false negative mails), addressed to email@example.com
False positives should be forwarded as an attachment (containing up to 10 false positive mails), addressed to firstname.lastname@example.org
Any CMAE feedback which arrives without an attachment or with too many attachments, will be ignored by the automated CMAE feedback system.
The CMAE feedback system is "reputation based", which means that if email@example.com consistently submits well formatted and timely feedback (ie., forwarded as attachment(s) and soon after delivery of the incorrectly classified message), their submissions will earn them a better reputation and be considered more reliable and trustworthy than firstname.lastname@example.org, whose feedback submissions are incorrectly formatted, or submitted a long time after receipt.
The sooner feedback reports are submitted, the better, but as the submitter’s trust-level is not affected by older mails, there is no problem with submitting feedback on old content.