I've been trying to setup my very own mail server for quite some time now. This has many benefits: cool domain name, 100% control, 100% privacy, etc...

But I've been struggling with that for way longer than my sysadmin title would let me admit.
I'm asking for help here, in case someone ever did it successfully in the past. My case is pretty common I think, so here is the context:

• One server, with one postfix instance
  
• One "main" domain: z3bra.org
  
• One virtual domain: domain.alt
  
• Ability to send mails from both domains
  

So far, sending mails from the main domain works great. My real problem comes from the virtual domain, as I can see that the mails leaving my server, but they either get bounced, spammed or even dropped without notice.
Google flags me as SPAM without giving a reason, and I managed to get the following error message from mail.com:

Quote:host mx01.mail.com[74.208.5.22] said: 550-Requested
action not taken: mailbox unavailable 550 invalid DNS MX or A/AAAA resource
record (in reply to MAIL FROM command)

All MX records for these domains are correct, and point to mail.<domain.tld>, which itself points to the IP address of my server.
The PTR record for this IP points to mail.z3bra.org. I tried adding another PTR record for the virtual domain, but it's still propagating and I'm not sure an IP can have multiple PTR records.

For what matters, all SPF records are ok for both domains (even goggle acknoledged it).

I'm now running out of ideas to get my mails delivered. This looks like an incorrect DNS setup, but I'm not sure what should be done at this point....

Please someone tell me you have an idea. I'm fairly sure the solution is simple!