Hi @vincenzopalazzo ,
Sorry to hear you are having issues with replying to an email.

Please report the error by pressing the 'Report' button on the error pop up if you have not already.
If you have a paid plan, please email customer support by using the support dialog inside the Tuta Mail client.

To use the support dialog, press 'Show Help' button () on the toolbar on the bottom left corner of the screen, then select 'Support'. The support dialog should appear and then you must write your problem into the text box. After some articles appear, scroll to the very bottom of the list & click the button labelled 'Contact support'.