Email delivery failure due to content restrictions

Brian Hadfield -

Chinook Communications scans all inbound email messages in an attempt to determine whether the message is valid or the message is spam.   If the mail filtering software believes that the message has a high likelihood of being spam, the message will be rejected with an error similar to the one below:   

550 5.7.1 Message rejected due to content restrictions

This error is generated when the mail message in question is being rejected based on the content of the message. In other words, the receiving mail server sees something in the content (or absent from the content) that makes it look like spam. Unfortunately, the message does not provide any detailed reporting on what parts of the message it sees as objectionable, so it can be hard to know what to change in order to avoid being blocked by content filters. Many times the objectionable content is in the signature and not the body of the e-mail, you may be able to get the message delivered by forwarding your e-mail again, but leave off the signature. If the e-mail is delivered, then you may consider a text only version of the signature. If the signature it not the problem, try forwarding the e-mail as text only.

Email from trusted senders is excluded from content filtering.  Adding a sender to your Outlook Safe Senders list will instruct the mail filtering service to allow the inbound message to be delivered regardless of content (all email is scanned for viruses).  To add a sender or domain to your Safe Senders list, see the Adding names to the Outlook Junk Email Filter lists article in our Support Forums.

Properly identifying mail as valid or spam is a constantly evolving process and as such, it is difficult to provide concrete examples of the types of content that are detected as spam.  There are some common characteristics of messages that increase the likelihood of the message being flagged as spam.  Avoiding these characteristic will add to the likelihood that an email message will be properly identified. 

Common characteristics that cause e-mails to be flagged as spam:

  1. Make sure you have a good text to image ratio. (Spam filters look skeptically upon emails that contain very little text but a large images)
  2.  Be aware of adding links in an e-mail, often signatures contain too many links (Spammers often send emails with little or no text and a link or numerous links)
  3. Write clean e-mails (Spam filters are keen to some of the more common spam formatting like red text in the body of the email or excessive use of underlining and bolding)
  4. Use a good subject line (Example of a bad subject line: DOWNLOAD FREE WHITEPAPER!!!)
  5. If your e-mail fails, try sending a text only version of the e-mail (Not only is this a good practice for avoiding a spam filter, but it also covers you in the case where the recipient cannot view HTML emails)
  6. Avoid sending large attachments or attachments of certain types (In general, .jpg, .gif, .png and .pdf attachments are safe to send, provided you include some content in the email as well. However, executable attachments such as .exe, .zip, .swf, etc. should be avoided entirely)


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