This is occurring on 3.1.0rc6. Basically the md5 hash that gets appended to assets when using image_tag is not present when used in ActionMailer views. So the resulting url does not work.
I created a vanilla rails app to make sure something I did isn't causing this.
Here is the result using the same erb view to render via ActionController and ActionMailer:
<img alt="Rails" src="/assets/rails-ccbe0ffcfe6f841608020ae576f7ac1c.png" />
=> <img alt="Rails" src="http://assets.example.com/assets/rails.png" />
Does this happen in 3.1.1 ?
@iamveen Are you still having this problem?
I'm closing this issue since it's pointing to a release candidate of 3.1 version, and got stale. Please let us know if you are able to reproduce this with 3-2 stable version, and we'll gladly reopen. Thanks!