??? Returned mail: see transcript for details ?

[Thilo Six]

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Hello

I got two mails like this:

The original message was received at Sun, 19 Feb 2006 22:05:37 +0100
from [lists.ubuntu.com]

- ----- The following addresses had permanent fatal errors -----
<kubuntu-users at lists.ubuntu.com>
(reason: 550 <kubuntu-users at lists.ubuntu.com>... Invalid recipient)

- ----- Transcript of session follows -----
.. while talking to lists.ubuntu.com.:

>>>>>> RCPT To:<kubuntu-users at lists.ubuntu.com>

<<< 550 <kubuntu-users at lists.ubuntu.com>... Invalid recipient
550 <kubuntu-users at lists.ubuntu.com>... Invalid recipient


What does it mean?
All my mails had reached the ML. So what is wrong?

bye Thilo
- --
i am on Ubuntu 2.6 KDE
- - some friend of mine
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