Secure Windows Email Client?

Hey I am looking for a secure email client for Windows. I haven't found anything really good except for "The Bat!" found. But I haven't looked far into it yet.

Currently I use Thunderbird and even though I'm really happy with it so far, I find Thunderbird's implementation of password protecting the client very strange and sketchy.

When I open the application, the first window I see is the password prompt.

But if I simply click it away, Thunderbird opens …

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