Let me try to explain this as concisely as possible...
I use Google Apps Premier for MOST of my domain email.
My DreamHost account is set with Custom MX records and I have checked the "I will still check my email at DreamHost" option so I can still set up and use mail accounts hosted by DreamHost.
I have Google Apps set to route incoming mail for unrecognized addresses to my DreamHost mail server "mx1.sub3.homie.mail.dreamhost.com"
With this setup almost everything works perfectly...google hosted accounts send and receive mail fine (using google servers), and DH hosted accounts do too (using DH mail servers).
HOWEVER, there is one particular problem...
If a DH hosted account sends mail to a Google hosted address at our domain, the following SMTP error is generated:
"Recipient address rejected: User unknown in virtual alias table."
Clearly the DH mail server is looking in its own records for the account and cant find it, despite the fact that our MX record is set for Google and it should be contacting Google to deliver the mail.
Anyone know how I can resolve this??
P.S. Interestingly, my web scripts hosted by dreamhost that send mail to my google-hosted addresses work fine...only sending from DH-hosted user to Google-hosted user via SMTP has the problem.