Sending email, especially on behalf of another company, comes with a ton of caveats and recommendations that we try to adhere to in an effort to avoid our domain getting blacklisted and added to spam lists. We made some changes to Ignition, so that all direct client emails come from the no-reply@ email address. 

This response was due to Google announcing a July 2016 launch date where they would start enforcing a strict DMARC policy (ie. rejecting all emails that aren't authorized to come from a nominated domain). The prospect of potentially having all client facing emails not reaching the intended address was enough for us to make some changes. 

In a nutshell it's a way for a mail server to check if an email has permission to be able to be send 'from' that domain. You can learn more about this here and here. 

If a client replies to a proposal sent from Ignition, the email address selected in the 'Display message from' field of the Presentation step in the proposal editor will be populated into the 'to' field of their email reply.