First try changing the Outgoing SMTP settings. Then the sender email, then the reply email.
Next I would contact your ISP technical support and find out what prohibitions they might have and ask them for a fix.
Lastly, I would try changing the port.
To do so in Outlook Express, go to TOOLS > ACCOUNTS >
Highlight your domain account, then click the PROPERTIES button.
You should see a tab (at the top and they look like file folder tabs) that says: Advanced. Click on it to bring it forward. You should see Outgoing Mail Port: 25
Change it to the number Will advised and then click Apply, then Okay, and close out of all the windows.
Then try your mail again with some test sends.
If all that doesn't work, contact Dreamhost Support. Maybe they have some suggestions. But I still think you ISP is your culprit if all the rest has failed. I have never had a client using either Outlook or Outlook Express with your similar difficulties that weren't resolved by jumping up and down on the ISP once all the settings were assured to be correct. It never involved changing the port settings...thus far.
Hope this gets things resolved. I'm crossing fingers and toes for you.
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