How do you "effortlessly reply" from any-email AT your_domain.tld?

I want to be able to send mail from any user@my_domain.tld.

And reply (seamlessly) from whatever address@my_domain.tld mail was sent to.

Sending: I am willing to edit some kind of FROM field for sending. Thunderbird desktop does this.

Replying: I want replying to be w/o *any* manual intervention (that of course excludes pre-adding an email like that in Apple Mail; or Thunderbird's "editable FROM" field).

Has anyone found a great/smooth solution for this?

Are mail forwarding services (e.g. SimpleLogin) better at this than mail hosts (e.g. Runbox)? Will I have to pay for both if I want this (because I believe forwarding services won't store my emails)?

(Apple's HideMyEmail is very restrictive esp. for "writing" an email and Duck.com doesn't even have a way to track which email is where)