I had the issue with email not reinstalling after backing it up a while ago. I used titanium backup, but it would not install. I tried putting it into the /system/apps and /data/apps and neither worked. In irc interdpth suggested using abd to push them to my phone and force install. nothing seemed to work. I just stopped trying because I only use gmail. So this may be a titanium backup problem?
Don't use Titanium backup to restore the stock email apk.
I uninstalled mine with Titanium backup and played around a bit and figured out how to reinstall it. It does require the apk and odex file that drfriggins has provided. (email.zip where he pulled the apk/odex straight outta his system/app)
I used root explorer to restore mine, but i'm sure any app like it will work.
Copy the email.apk/odex to your Sd.
Copy them one at a time into system/app.
EDIT the permissions on the apk and the odex to be user read/write, group/other read. You can check all other items in the app folder, they will have the same permission setup.
Make sure you have your 'com.android.email.apk' in the system/app folder. I uninstalled my email app with Titanium and it left the com.android file there, though it could have just been installed with gmail.. but just check and make sure you have one.
Once you've copied and set permissions on the apk/odex and made sure you have your com.android.email.apk, just reboot your phone and check your app folder.
Your stock email should have reinstalled and appear.
*****EDIT*****
Remember to set R/W permissions with your root explorer program before copying and editing the permissions.
To edit permissions (I only know how to set them with the root explorer app, your app might have a different way) just long click and select permissions from the options that come up.