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Mail error 421 Excessive failed authentication, ESMTP server temporarily not available, please conta

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Mail error 421 Excessive failed authentication, ESMTP server temporarily not available, please conta

I was getting an error message last night when trying to send from one of my comcast.net addresses today.  Using outlook 2013.  

 

"reported error (0x800CCC67):  The server responded:  421 resomta-po-13v.sys.comcast.net resomta-po-13v.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available, please contact support."

 

Things seem to be working now, but should I be concerned?