What support address are email replies sent from? Why does the reply address not match the support address it was sent to?
Email replies are sent from the support address they are received at. 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 the Support addresses page. For example, tickets created through Talk, Chat, or API. If you would like to change the support address used for the reply, the Select an Address app provides this functionality.