First of all IE and NN are not mail programs, they are Internet browsers. If you are using an internet based mail program (like you have to launch your browser to check your email), that program is actually software that someone created and it is sitting on their server, somewhere. They may not have thouroughly tested their software before releasing it, or they may have only created the software with intentions of using it with IE.

Also, IE is a stronger browser as far as functionality. If there is a missing HTML tag, it will automatically figure out what tag is missing, and where place the proper tag where it should be placed. Netscape doesn't have this feature. If a tag is missing in Netscape, then it will break the whole page.

If you are actually talking about Netscape's mail program (the one that sits on your desktop and can be launched without launching the internet) and Outlook Express by Microsoft, then the same sort of thing applies... they are different software written by different teams of programers with different goals and objectives. Again, Netscape's software is not as strong as Microsoft's, and it could be that Netscape simply hasn't created a version of their mail program that supports SWFs or animated GIFs in email correspondance.

You see?