IM's?
Instant messages.
All of Foley's sexually explicit correspondence (so far revealed) was in the form of instant messages sent under the alias maf54 (Mark A Foley, born 1954).
As far as I know, there are no sexually explicit emails.
Now, the emails he sent which have been disclosed, viewed in the light of the recently revealed IMs, constitute obvious trolling.
But without the IMs, a boss or supervisor (and Hastert is neither) is in a tough spot to INTERPRET the emails as sexual in nature, UNLESS said boss or supervisor a) knows Foley is gay, and b) is willing to hold a gay man to a different standard than he would a normal man.