TABLE 3.

Testing protocol.

Step 1	Interview of the participants covering: Demographic information (age, nationality, profession), preferred mail user agent, and previous knowledge about cryptography and e-mail encryption
Step 2 (if needed)	Installation of mail user agent and configuration of mail access through IMAP with supervisor help
Step 3	Participants are asked to send an encrypted and signed e-mail to the supervisor using one of the following encryption technologies. The instructions were adapted according idiosyncrasies of the tools employed by the user as shown below
	PGP
	Instructions	For FlowCrypt: no further information
		For Thunderbird: install Enigmail plugin, activate setting “enforce PGP and S/MIME”
		For Outlook: install gp4o plugin
		For Android: install Maildroid (mail reader) and CryptoPlugin (key administration)
	Goal	To send encrypted and signed e-mail + compare key fingerprints
	S/MIME
	Instructions	For all: Obtain a certificate from: https://extrassl.actalis.it/portal/uapub/free-mail?lang=en
		For Thunderbird: no further information
		For Outlook: go to “trust center settings” for importing the certificate
		For Android: install Maildroid (mail reader) and CryptoPlugin (certificate administration)
		For Apple-mail: no specific recommendation
	Goal	To send encrypted and signed e-mail
	pEp
	Instructions	For Thunderbird: active “enforce pretty easy privacy” setting
		For Android: install pEp official Android app
	Goal	To send secure e-mail + execute handshake

The bold values to distinguish the names of the different mail user agent (MUA).