What could be more personal to a vendor than that of a real human handwritten letter, complete with fountain pen ink and aesthetically pleasing paper to boot?

Well, it's as personal as it gets. The only issue is that it takes time, a lot of time, to individually handwrite letters that are unique and bespoke to each vendor. 

That is where LetterBot.co.uk comes in. They utilise a robotic arm to outsource this for you:

PSEngine integrates DIRECTLY so that you can send handwritten letters at the click of a button. To do so, simply fill in the form on the button below to 'order' your templates and API key for the software.

Once you have your API key open Config | Letterbot from within the software and add your API details. You can add multiple if you would like to keep multiple accounts separate.

All of your templates that you have setup with LetterBot will now be accessible from within the Send Dialog. Also, remember that when you create your templates, you can add wildcard fields from the software that take the format under Config | Letter Config:

These are covered further within the Wildcard Field article within features.