remove Text or Word-Passages in the Mailtext

Postie has features to trim the start or end of your email if there is consistent text. See https://postieplugin.com/ufaq/specifying-the-beginning-of-the-post/ and https://postieplugin.com/ufaq/specifying-the-end-of-the-post/

There is also a feature for removing email signatures.

You can also build your own logic via a custom addon. See https://postieplugin.com/extending/