We just rolled out a migration of a VM pro server. The only significant differnce is that we upgraded the OS from Deb 5 to Deb 6 in the process.
Everything looks to be working fine with one frequent exception in the mail logs
Nov 4 18:04:55 lamphost1 postfix/smtp: 143C27292F: firstname.lastname@example.org, orig_to=xxxxx@xxxxx.COM, relay=gmail-smtp-in.l.google.com[188.8.131.52]:25, delay=1, delays=0.33/0/0.19/0.49, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[184.108.40.206] said: 550-5.7.1 [xx.xx.xx.xx] The IP you’re using to send mail is not authorized to 550-5.7.1 send email directly to our servers. Please use the SMTP relay at your 550-5.7.1 service provider instead. Learn more at 550 5.7.1 http://mail.google.com/support/bin/answer.py?answer=10336 r8si1735123ybf.44 (in reply to end of DATA command))
The virtualmin install was with the install.sh script and Postfix was configured exactly as was the server this box took over for - with the exception of hostname, ip, etc. But on the old server we never had this problem with Gmail outright rejecting everything from us.
I’ve check to see if the server is blacklisted for any reason and it is not.