To overwrite any of the mailer stuff, you have to bring it into your local.
there is a generator for it
however, there are a few issues all saying that part of it is broken
here is one that found a workaround #306
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I need to go through and fix stuff like this but am swamped, as are the other maintainers. if you find anything like this and want to submit a pull request, please do and i will pull it in as soon as i can.