When writing an email, show the signature and if possible be able to modify it. Displaying it allows you to be sure that it is taken into account and to check its content. Practical when you sometimes switch between two responsibilities on the same mailing address. Being able to modify it at this level would allow for a one-time sending to be able to manage its content. The aim is not for the modification to be recorded for future shipments, but for a one-off change.