If none of the more obvious "Moderate" settings shows up as the problem, you might check your Attachments setting (in Message Formatting). One of the options there is to Moderate them - that is, someone would have to "okay" any messages that contain attachments. Emails with attached "cards" or those that use stationery designs could be showing up there. A URL by itself doesn't typically show as an attachment, but if there is a "preview" along with it, that could.
Barb
