A friend has suddenly lost the ability send email. The OS is XP and OE6

The gist of the error message follows:
smtp.comcast,net propotcol:smtp, server response 554 ....port:587,secure
ssl: no,server error:554, error number:0x800ccc6f

Comcast has walked the user through the setup for email and it agrees with
my own setup.

System was rebooted with no change.

What now?