There's a file on my web site called dead.letter. It's about 10 meg in size. Any idea what it is and if I can delete it safely?

I have always found this file to be email messages that one of the scripts on my site has tried to send but sendmail was not able to deliver. You can open it up in text editor and see what emails where not going through to try and figure out what was failing. It is safe to delete. If for some reason sendmail can't send again in the future then it simply creates the file again. Not sure if I have all the technical language right then or if a script trying to send mail that can not be delivered is the only cause but I do know you can delete it with no adverse effects... I have done it many times when I have had something set wrong on scripts. The times it happened with me was when I was I had entered and alias email account instead of a real email account into the script.