Okay, amend that a bit. I checked with an epidemiology study done by UCLA and got the "definitive" (i.e., best guess) list of letters. There were five letters mailed 9/18, exactly one week after 9/11. All five were sent to the media: American Media, the NY Post, NBC, ABC and CBS. The Daschle and Leahy letters, which contained superior anthrax and a different message, were mailed 10/9.
The aforementioned study, by the way, is very much worth reading. It also contains a link to another excellent site, anthraxinvestigation.com. That site's author is altogether too quick to pooh-pooh the al-Qaeda and Iraq links, but aside from that he's written a lot of thought-provoking material.
The editor of The Sun, Michael Irish, is a private pilot who flies out of the Lantana airfield where Mohammed Atta practiced for the WTC attacks. His wife, Gloria Irish, is a realtor who found apartments near AMI for several of the hijackers, and had numerous contacts with them in the run-up to their destruction of the World Trade Center.
The FBI chooses not to discuss or explore the AMI incident on the AMERITHRAX web-site. AMI officials believe the FBI has not been frank with AMI's employees about the nature of the attack, and discounts the domestic loner premise which is, for public consumption at least, the focus of the AMERITHRAX investigation.