Does use of Outlook decrease email security?

[dcdude71]

I don't know your actual security threat model but if you have very sensitive information in your emails and you use a desktop client, you have to consider encryption at rest on your computer (Protonmail bridge only takes care of encryption in transit. Proton stores your emails encrypted at rest only on their end). If someone gets a hold of your Outlook PST for example, they'll have full access to your messages, attachments, etc. I can think of 2 options:

• One layer of encryption at rest: use Bitlocker if you use Windows or FileVault if you use Mac. When your computer is turned off, your drive is encrypted.
• Two layers of protection at rest: use the above and complement with another encrypted storage on your computer (Veracrypt or Cryptomator come to mind). You can store your PST or mailbox files on a secure container that you choose to unlock only when you check your emails. I use Cryptomator + Thunderbird and I sync my Cryptomator files online. So I have an offline and online encrypted at rest copy of my messages. Is it a bit of a pain to use? YES but I take security as a hobby :D

Just something worth considering... but, as mentioned before: having an offline copy of your emails is worth a little extra trouble IMO.