How to downgrade a particular package?

[pyramidX]

In http://stackoverflow.com/a/23866880/779159 there's a workaround to some pyramid_mailer issue by downgrading repoze.sendmail from 4.2 to 4.1. How can I do this?

All I did was follow instructions at https://github.com/Pylons/pyramid_mailer/blob/master/docs/index.rst#getting-started-the-easier-way and added

pyramid.includes =
   pyramid_mailer

and

config.include('pyramid_mailer')

I didn't do anything with repoze.sendmail. How can I implement the suggested workaround? Can I somehow specify the version in setup.py?

[Jonathan Vanasco]

commandline

    $ pip install pyramid_mailer==4.1

setup.py:

install_requires = ['pyramid_mailer ==4.1']