Short answer: No.
Long answer:
A user writes something on Drupal Community, and someone [Y] replies with a post either on Drupal Community or through a Drupal Community private message (PM). Thus, Drupal Community will normally notify user about this message automatically through an email.
Now, if the user wants to respond, MUST do it either on Drupal Community itself, as a new post, sending a [PM], or by clicking over the link of the email this user got, where it says ‘Visit [Message|Topic] to respond’.
Users NEVER should try to reply the message through email, otherwise this message never will be delivered and after some time, a notification like the following one will be received:
Delivery is delayed to these recipients or groups:
Some User (noreply@drupal-community.web.cern.ch)
Subject: RE: [Drupal Community] Xxxx xxxx xxx xxx
This message hasn’t been delivered yet. Delivery will continue to be attempted.
The server will keep trying to deliver this message for the next 1 days, 19 hours and 52 minutes. You’ll be notified if the message can’t be delivered by that time.