can anyone explain to me what this error means, why it occurs and its
solution. I got this error for All my list members using hotmail.

<<--> Error description:
 Error-for:  [log in to unmask]
 Error-Code: 3
 Error-Text: Mailer "mc4.law5.HOTMAIL.COM" permanently refused service (5xx
             reply to HELO)>>

 Yoseph