Password response in Malitwasher -strange!

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I introduced to-day another of my friends to Mailwasher and the installation
went without any problems.

Only when he downloaded (or wanted to) messages the Sign-on window came up
with his Username and Password already in it. But then a notice:

"Authentication failed. Plaintext passwords not supported for this account"

He uses Verizon for his ISP, same as I, and I have never seen this message.

I went to mailwasher's FAQ and read all of them, but this is not explained.

What does it mean and what does he need to do?

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