I´m new here so maybe I´m posting this in the wrong area. Accept my apologies for that.
I noticed the following phenomenon. I received an email with 3 letters followed by a colon in the subject line. After the colon there was a space and then some more information. When I answered to this email, the 2 letters and the colon disappeared but everything else remained in the subject line. An AW: was added in front of course. We used this 3 letter code for our customer followed by the subject. When answering ony the subject is left but the customer code is gone. I tried it with 4 letters - no problem. I left away the colon - no error.