outlook invitation with html not rendered correctly

I'm trying to send a nicely formatted email with an iCalendar to a user who's using outlook 2010, but the result is horrible. If the file is removed everything looks great.

I thought I was doing something wrong, so I've tried the same scenario using Google's calendar and got the same result.

In following image, on the right side you can see how Google's HTML is all messed up when it arrives from server. on the left side, I've saved the email as eml changed the invitation mime-type to something else and the email is fixed:

You may find the sample two EML files here on GitHub:

original_mail

fixed_mail_invite_not_working

As you'll see, the only difference is the calendar mime in line 172.

Does any one have any ideas why is this happening? is there a workaround?? or a fix?

Update: one of our clients sent me a screen-shot of his outlook, in this case you may see that outlook displays the HTML better and also process the event... any ideas?

Outlook internally uses RTF for the appointments, tasks and contacts, so your HTML will always be (imperfectly) converted to RTF.

There isn't much you can do besides tweaking your HTML until Outlook likes it.