Mailer-daemon (Falsely) Says Email Full

Today I received this email from:

mailer-daeomonatcomcastdotnet

      "This is an automatically generated Delivery Status Notification.     

Delivery to the following recipients failed permanently:

   *I deleted the email name that was shown here, but it was to my daughter who uses a comcast email address

Reason: recipient mailbox full"

Problem is, her web email is less than 10% full.  She uses a client email program on both her phone and laptop, and has it set to delete emails when downloaded.  And again, her comcast web email is less than 10% full.

I see many similar posts regarding this, but no solutions.  What's going on?

Thanks.