Fake Image using .aspx url to track email views in Outlook, doesn't work!

I have this in my HTML email to 开发者_运维问答track if someone views the email in say Outlook.

<img src="http://www.example.com/track.ashx?user=3434" />

but this doesn't seem to work.

Should I change my headers in the .ashx to server image headers? (if there are any?)

Can this work using this method?

I emailed myself with an email, other images displayed properly. There was no log in the database for the handler (the handler logs all requests to the db). Calling the URL to the file in the browser logs to the db, so its working.

What testing have you done? A lot of email clients these days don't download images associated with an email unless the user explicitly requests it or adds the sender to a whitelist. It's possible your HTML and server are all correct, but the client just isn't attempting to go to the URL.

Are the email clients set to display pictures? Many don't by default.