If you enable this module, the "From" address on contact emails, both site emails via the contact form and user-to-user emails via the member contact form, will be "From" the email address configured in site_mail (admin/config/system/site-information in d7). The reply-to header will be set to the address that Drupal would have used as the From address.

Note that Drupal 8 has this feature in core (see #111702: Set fixed "from:" and add "Reply-to:" to comply with DMARC), so this module is not needed in D8 and no D8 port is planned.

This avoids many spam-classification issues. Many, many mail handlers will classify as spam a mail that comes from an unauthorized location, as this is spoofing. What Drupal does by default is spoofing...

Dreamhost actually *prevents* the sending of Drupal emails in many cases. This module should resolve that problem, but it's a problem elsewhere almost everywhere the Drupal contact form is used.

If you don't mind using a 3rd party service and have a nontrivial site, you'll probably enjoy the mandrill module and service. If you're on Dreamhost shared hosting, though, it probably means you have a trivial site to maintain and Mandrill would be overkill and additional complexity.

Note that this is not just a Dreamhost problem. The issue with Dreamhost happens on the sending end, but with many, many mail providers, your contact form mail from Drupal will be classified as spam because it's coming from a source not authorized by the sending domain. For example, if somebody puts me@example.com in the contact form (or has that for their user email) then normally Drupal will try to send as me@example.com. Any decent email spam system will check the SPF record for example.com, note that your server IP is not listed there, and downgrade the email as a result. Also, since the email doesn't have DKIM headers, which most reputable senders now have, it gets a downgrade for that as well.

Finally, please note that it is *still* your obligation to make sure that your site_mail email address is properly configured with regard to SPF and DKIM. On Dreamhost, you will need to make sure that Dreamhost is responsible for the site_mail domain and address, or use other methods to send mail.

And... not every email client handles reply-to: correctly, even though it has been deployed since the beginning of email. Yahoo Mail in particular seems to ignore it. That doesn't matter much for the site contact form, but can be important with user-to-user contacts.

Other ideas on other ways to resolve this problem are certainly welcome in the issue queue and will be mentioned here.