[ruby-core:67772] Preventing Redundant Email Messages

For a long time, I've wondered why I sometimes receive redundant email
messages when a ticket is updated in Redmine.  For example, just a few
minutes ago:

[ruby-core:67768] Re: [ruby-trunk - Misc #10754] Tiny optimisation of Set#include?
[ruby-core:67769] [ruby-trunk - Misc #10754] Tiny optimisation of Set#include?

The first one appears to be Erik's response (coming from Eric's email
server), and the second one is a ticket update from Redmine (coming
from an application running on Heroku via Sendgrid).

I'm guessing that the scenario is: Eric responds to an email, and there
is a program running which takes his response, updates a ticket, and
updating a ticket sends out another response.  Assuming that is the
case, is there any way to avoid this?  Can we have the program that
updates the ticket set a flag to not send out the duplicate email?
Or change something so that Eric's initial email is not sent out to
ruby-core, it just updates a ticket, which causes the second email to
be sent out?

Thanks,
Jeremy