The reason this is occuring is because some spam filtering software is screening E-Mail for the "X-library:" header. This header is sent by Indy 8.0 and the release versions of Indy 9.0. In and of itself, this is not bad. However, some malware such as spam bulk E-Mails and even a worm (W32/Nicehello@MM), were built with Indy meaning that they sent the same "X-Library:" header that most Indy-based E-Mail programs do.
For this reason, we have decided to remove the X-Library header from Indy 9.0 code and you can obtain it from our VCS.