Requested mail action › Question about Outlook Express

Unable to Send to Hotmail.com 550 Requested Action not taken. Mail from:

Our client is unable to send emails to Hotmail.com (was working last week).

This is the error our client's exchange server comes back with. We have confirmed the Hotmail account works and it live.

Requested #550 Requested action not taken: mailbox unavailable ##

It appears MS are blocking our domain as telnet email fails (see below). The same telnet commands work when not using the client's network.

220 BAY0-MC4-F17.Bay0.hotmail.com Service ready

helo ahmrc.org.au

250 Requested mail action okay, completed

mail from:******@ahmrc.org.au

550 Requested action not taken: mailbox unavailable

Connection to host lost.

Is anyone able to assist? It appears MS are blocking our clients request to send email to Hotmail.com