I found where it is stored, created some of my own, but it isn't intuitive and certainly not fool proof
The basic templates are stored here:
/Library/Application Support/Apple/Mail/Stationery/Apple/Contents/Resources/
Each sub directory has a TableOfContents.plist and each stationery has a UID.
The first thing I did was copy the /Library/Application Support/Apple/Mail/Stationery/Apple directory to /Library/Application Support/Apple/Mail/Stationery/Mine. This resulted in two of everything.
I have been experimenting with one of the Photos templates and had some success. The file content.html has the basic html, however I have had mixed success replacing the default photos. Apple has created some magic that I don't understand. I replace the three files placeholderX.jpg with three of my own, the result was good for two, but it went off and found a completely different picture for the third.
This is clearly a great opportunity for an application to create stationery.
The basic templates are stored here:
/Library/Application Support/Apple/Mail/Stationery/Apple/Contents/Resources/
Each sub directory has a TableOfContents.plist and each stationery has a UID.
The first thing I did was copy the /Library/Application Support/Apple/Mail/Stationery/Apple directory to /Library/Application Support/Apple/Mail/Stationery/Mine. This resulted in two of everything.
I have been experimenting with one of the Photos templates and had some success. The file content.html has the basic html, however I have had mixed success replacing the default photos. Apple has created some magic that I don't understand. I replace the three files placeholderX.jpg with three of my own, the result was good for two, but it went off and found a completely different picture for the third.
This is clearly a great opportunity for an application to create stationery.