EMail Router error message

[MRo]

Hello!

We configured about 100 POP3 mailboxes and corresponding queues in MS CRM
4.0 which are used by the email router for receiving emails. When testing the
queue definitions in the email router we get error messages for approximately
50 of these queues but for each run of the test, other queues are marked as
error. ´

The error message says

"Incoming Status: Failure - An error occured while executing POP3 command
"<Command removed for security reasons>". The server response was: "-ERR
Command not valid".

OR

"Incoming Status: Failure - An error occured while executing POP3 command
"<Command removed for security reasons>". The server response was: "-ERR
Logon Failure".

Also the event log shows these errors, e.g.:

#26090 - An error occured while opening mailbox X...@test.com.
Microsoft.Crm.Tools.Email.Providers.EmailException: An error occured while
executing POP3 command "<Command removed for security reasons>". The server
response was: "-ERR logon Failure". at
Microsoft.Crm.Tools.Email.Providers.Pop3Client.ValidateLine(StringreceivedLine,
String command, Boolean hideCommand) at
Microsoft.Crm.Tools.Email.Providers.Pop3Client.ReadDataWithEncoding(StreamReader streamReader,String command, Boolean
...

Does anyone already know that issue?

Thanks a lot!
Martha