Update: The link pointed to by the "duplicate" initially didn't seem like the same problem to me, because the post talked about blacklisted "domains" not blacklisted "IP addresses."
However the main solution is the same: If you are going to forward to Google, you need to install an anti-spam solution of some sort. Even if you don't run an open relay, the degree of spam sent to any domain in the world is staggering, and you will be dinged for it.
Integrating Spamassassin, and making sure SPF works for my vanity domains, worked fine for me. I just send anything with a spam score of 5 or higher to /var/spool/spam (I created this directory) rather than forwarding it, and have a cron script that deletes anything in that directory older than 30 days.
previous quesiton
I have a few vanity domain names, some of which have MX records that point to a virtual private server that runs postfix, which in turn forwards email to user accounts at gmail. Unfortunately, internet spam being what it is, Google will tell my postfix that it is rate limiting because of sending a lot of spam. Specifically, the status message mentions that it's the IP that gets a bad reputation. Previous messages I've found have dealt with domains getting a bad reputation.
I've tried following the instructions in the Google postmaster links, but this doesn't really help:
//www.google.com/mail/help/bulk_mail.html
After all -- I'm not the sender; I'm just a mail server operator where users choose to forward email to gmail.
As usual, it is impossible to get to talk to a human being at Google who can help me figure out how to make this work, and gmail doesn't support free vanity domain accounts anymore, so I'm turning to this community of system and network administrators, where perhaps someone else has some good ideas? How can I get mail delivered to my-vanity-domain.com on my-vps-ip.net, and then forwarded to a gmail user account, to not get my-vps-ip.net classified as "spam sender"?