It sometimes happens when I reply to an e-mail from somebody who is asking about my products that the receiving mail server rejects my message with the code “554 rejected due to spam content”.
Google Apps notifies about that like this:
Vintage Ad #906 by jbcurio under CC
When that happens I try to send the message from another e-mail account. That works in some cases, but not always. Sometimes the second attempt fails, too, although the second message was sent from a different domain with a different mail server, whose notification looks like this:
Obviously, this has nothing to do with my mail system. These are false positives where the receiving mail server finds something in my e-mails it does not like – but what? I had not attached anything and the messages were just a few lines of text.
As it turned out some security products do not like URLs in e-mails. In all cases my messages went through once I removed any links I had added. In cases where my messages did not contain any links I removed the URL to my website in the signature.
The post Workaround: “554 rejected due to spam content” sending e-mail is original content of Helge Klein - Tools for IT Pros.