[shuzchen]

You might be interested in https://github.com/zedshaw/lamson It's super old (died when python 2 was still the king) but probably more suited for making programmatic mail applications

[jfkw]

There is an active lamson fork https://github.com/moggers87/salmon that retains the original GPL license and supports current Python 2.x and 3.x versions.

[datashaman]

Difficult to search for, so I'll ask on the chance that you know: I see .vel files in that repository. Do you know anything about what language or format that is?

[shuzchen]

https://pypi.org/project/vellum/ https://launchpad.net/vellum

[cbsks]

They look like configure files for a python build script:

https://github.com/zedshaw/vellum