We have emails sent to people within our company that are filtered into Outlook's Junk Mail. Basically, there is a signup form on our company's .Net website, and when people signup, these automated messages are sent.
This is confusing, because everything happens within our Windows domain. I do not know why Outlook would block mail within our own domain.
Even stranger, this behavior changes based in the "From" address. I can fix the problem by using the From address "email@example.com" but the mail gets blocked when I try other From addresses. The From Addresses I tried and failed are: "firstname.lastname@example.org", "email@example.com", or "firstname.lastname@example.org".
The text within the email seems very benign, in that I see nothing that a Spam content filter would want to block. If I could just use "email@example.com" as our from address everything would be fine. But I can't use that address, so emails continue to get blocked for no apparent reason.