What support address are email replies sent from?
Email replies are sent from the support address they are received. If you are experiencing delivery issues like messages going to junk or SPAM, see the article: Allowing Zendesk to send email on behalf of your email domain.
For tickets not created by email, replies are sent from the default address set in Admin > Channels > Email. If you would like to change the support address used for the reply, the Select an Address app provides this functionality.