To add a Jotform form to your Posterous blog post, you will need to use the IFrame Code.
To get the IFrame code, on the Jotform Form Builder:
1. Click on “Publish”
2. Click on “Embed” and then click on “iFrame” option
3. Copy the form code.
Then click on “HTML” button on Posterous and paste the form iframe code in it.
It removes the height element from the code the first time. So, you will need to edit the post again and add or whatever the size of your form is manual.