Hello, I just installed Zimbra and works great!!!, when I tried to acces my mail have the same problem, Outlook, keeps asking for my password.
After some little debug, I noticed that Zimbra uses TLS for their conections, so you only have to activate TLS.
You can use some Open Source Mail like Thunderbird, that work very well with Zimbra, and support PGP also!!.
Cheers
Diego R.Garcia
SOFTNS S.A.C
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