If you use fastmail and a custom domain it automagically lets you reply to email from the email they sent you. i.e. if you have COMPANYA@mydomain.com and you reply to one of their emails it comes from COMPANYA@mydomain.com

Most paid email providers let you setup a custom domain with a catch all address, its worth it. Not all have this handy reply email feature, and you have to configure a custom response address, annoying it but works too