.exe files are executable files and are often refused by servers when attached to an email. You could try zipping it into a file (extension .zip) but some servers still note the .exe extension within the compressed file and refuse to let it pass through their hands.

I know what an exe file is and that they are potentially dangerous. Same with zip files, and as far as that goes, files with the extension "zzz", "aaa" or anything else. My problem is that until today I have been able to send out an email with an exe file attached. I need to know if thunderbird has changed *IT'S* policies concerning this, or whether it is my antivirus or internet provider that has changed their policy so that I can work with whoever has changed it, and what is still acceptable. Sorry if I sound angry, but I am. This is something that didn't happen yesterday, and is happening today, and one of the players involved has changed the rules. I just want to know who and what the new rules are.