550 Denied due to spam list

[axslingr]

That usually means you need to enable smtp authentication in your email client.

Lance

[pandreas21]

One way to get rid of these messages is to route your outgoing email though your provider's smtp's.

You are looking for sendmail's SMARTHOST functionality.

Rgds

[Jakes]

Are you currently routing through a smart host or are you doing direct delivery?
If you are doing direct delivery you should check if your mail server IP appears on any blacklists before routing through your ISP and sort out what caused you to be blacklisted in the first place. Try http://www.mxtoolbox.com/blacklists.aspx
How long ago did the problem start? If it is recent development other locations may start refusing mail from you as well.

Jakes