Previously, I discussed how to create custom CSS email signatures for Mail in Mac OS X. This week, we are going to take a look at what it takes to replicate the same signature on your iPhone.

What You Will Need

• Your Mac
• Your iPhone (it needs to be jailbroken)
• PlistEdit Pro (or another application capable of editing plists)
• Coda (or another application for editing HTML)

Before We Begin

To use a custom CSS signature, we will be modifying a preference file on your iPhone. Simply using copy and paste within the new 3.0 OS will not maintain the HTML and formatting of our signature. Your iPhone should already be jailbroken and capable of mounting as an Apple File Protocol (AFP) share on your Mac. For instructions on this process, see here.

Step One

Once you have logged into your iPhone over AFP, browse to the following location:

/private/var/mobile/Library/Preferences

Copy the file com.apple.mobilemail.plist to your Mac. Go ahead and duplicate this file, appending “backup” to the end of the filename so you have a clean copy in case something goes wrong.

Step Two

Open your email signature that we created (see the original post here) in your HTML editor and copy the contents to the clipboard.

Step Three

Use PlistEdit Pro to open the file you coped earlier in Step One. Towards the bottom of the list, you will see an entry called “SignatureKey”. The value for this string will match your current iPhone signature.

Double click this value to highlight the contents and delete what is there. Now paste the HTML code for your email signature that we copied in Step Two. Save this file back to your desktop.

Step Four

Browse back to the Preferences folder on your iPhone. Copy our new edited plist file and replace the original on your iPhone.

Step Five

All done! Create a new email and you should see your HTML email signature at the bottom.

Limitations

Unfortunately due to limitations in the iPhone 3.0 OS, Mail on the iPhone only supports one signature. There are third party applications available on the App Store that address this issue, but I have not tested them with HTML email signatures. Hopefully in a future OS update, Apple will allow users to have unique signatures for multiple mail accounts.

This process and file location has remained the same since iPhone OS 1.1.4 and will likely remain the same, meaning as new OS updates come out, they should not break this functionality (unless Apple adds support for multiple signatures at some point). However, if an update does break your signature, the process outlined above should still work to put it back.