What ever it means, it at least means "trouble" --  Send the customer a
separate email explaining that it occurred as a result of recent
list-distributions.  Ask them if they are aware of any problems.
Depending upon the (automated?) response, act appropriately.

At 04:46 03/04/1999 Thursday -0500, you wrote:
|Lately I have been getting the error msg.:
|
|550 System resources error: 104
|
|from some hotmail addresses.  Anybody know what this means?  Unknown
|user, over quota, ...?