@girish I appreciate the thoughtful response and research with your answers! I'm aware of the subaddresses and have used that through Gmail and such, but really love the simplicity of the catch all. I was able to get this functionality working through RainLoop, though not dynamically, as you mentioned. Under RainLoop -> Settings -> Accounts, one can add 'Identities' which consist of an email (where you can use addresses such as store1@domain.com) and a name. When one of these Identities' addresses lines up with an email, hitting reply will automatically select that identity as the FROM on your response email. Handy! Looks like Airmail (my Mac email client) also has 'Email Aliases' that is probably similar. While not automatic for any catch all address, this will give me what I need on the rare occasions I do need to respond from not my mail address. Thanks again! [resolved]