html file not found

I've just designed an html mailshot to be embedded into a bulk email. I need a link at the top which displays the email in a web browser incase security settings in the mail app prevent images being displayed etc. I have been given the ftp details for the customers website so i can upload the html file but it says file not found when i type the domain/mailshot.html. It is in the root directory and i've also tried it in the folder the website is held in, called htdocs. The website is all done in php, which i'm not familiar with. Could the webspace be setup for php only? I dont understand why the html file is not found. I don't really want to post the customer URL here as this forum post will show up in google if customers search for them, but i can PM the url if necessary. Does anyone have any ideas as to why the html file is not found? thanks in advance, Dren.