Illegal IMail List Server Command!

[List Server]

IMail List Server for Windows NT, Ipswitch, Inc. 
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   Valid Commands are:

   To subscribe to a list, send a mail message to "imailsrv" at
   this address with the following in the body of the message:

   subscribe listname your_full_name

   To unsubscribe from a list, send a mail message to "imailsrv" at
   this address with the following in the body of the message:

   unsubscribe listname

   To receive a list of the lists supported here:

   list

   To receive a list of users on a given list
   (If enabled for that particular list):

   list listname

   To receive help send:

   help [listname]

   To change to digest mode, send a mail message to "imailsrv" at
   this address with the following in the body of the message:

   set mode digest listname

   To change back to standard mode, send a mail message to "imailsrv" at
   this address with the following in the body of the message:

   set mode standard listname