Rated 4 out of 5 stars

Must have addon, but need "Reply All" button

This review is for a previous version of the add-on (2.0.7).  This user has a previous review of this add-on.

You can right click on the header toolbar and "customize" it: Then you can add or remove buttons. The reply all button is in the default set (click the corresponding button in the customization dialog or add it by drag and drop).