Some of our customers who have been checking their email campaigns in our Inbox Inspector  are noticing that Postini is a very, very tough email firewall to get through. Just about everybody (including us!) is getting rejected by Postini.

Dozens of our customers have been testing their campaigns, but so far, we’ve only seen about 8 campaigns actually get through Postini. Ouch!

You may recall I spent hours dueling with Postini with this GourmetStation campaign. I changed keywords, altered the HTML, totally changed the subject line—all to no avail (at least I made a pretty fascinating image-to-text discovery).

Postini is very picky. Smart—but picky.

All I can say is that if you’re having trouble getting through Postini’s firewall, below are screenshots of some campaigns that actually passed. Maybe you’ll see some kind of pattern here…

The only general similarity I can see with all these campaigns is their image-to-weight ratio.

If they have lots of images, they need a lot more text to balance things out. If a campaign has very little text, then it better not have a lot of images. Also, these people are experienced (maybe a little obsessed) with coding clean HTML (or they simply used our built-in HTML email templates).

Big thanks to all these MailChimp customers for letting us learn from their campaigns…

RealTruck.com Mother’s Day Campaign
What’s surprising to me about this one from RealTruck.com is it actually contains lots of those "spammy" keywords that we’ve all been trained to avoid. They used words like NEW, and You Save. They also use red text, and have dollar signs galore. But they got a 100% pass for their Spam Filter score. Goes to show the spam filters are a lot smarter than you think, and the old advice of "Avoid spammy words" just doesn’t always work. So long as you’re sending good, useful email that people actually requested, you don’t have to stress over every little keyword in your campaign.

SoupStudios.com Mother’s Day Campaign
Here’s one from Aarron Walter, designed for Soup Studios. This is a campaign that doesn’t have a lot of text in it, so you’d think the spam filters would give him some grief. Aarron’s a web developer, and his code is spotless. That probably helped a lot (certainly didn’t hurt him!). Also, the image is well optimized at 40k.  Aarron knows what he’s doing, and somehow, I think Postini picked up on that.

Robb Report Home Entertainment eNews
This one from Robb Report has 4 big images in it, but it’s also got a lot of text in it to balance them out. Plus, the text is quality content. Product reviews with no apparent "CLICK HERE NOW!" keywords. Note: I spoke with their designer, and she apparently spends a lot of time making sure their HTML code is immaculate before copy-pasting into MailChimp.

Caitlin Allen Acupuncture
I get a lot of "pharmaceutical" spam, so if you were to tell me an email campaign with, "Chinese medicine, Chinese herbs, hayfever, rhinitis, pilates, bloating, and probiotics" could ever pass through spam filters, I’d ask you what kind of crack you were smoking. But Caitlin Allen Acupuncture sent this nice, well-written newsletter to their customers, with ALL those pharmaceutical keywords (and more) and got a 100% passing score. The spam filters (including Postini) could tell that this was good, useful content, so they didn’t block it.

LBC Wise Counsel
This one’s from Oomph Design, on behalf of their client, LBC Wise Counsel. I like this one for several reasons. First, they passed Postini. Second, they used one of our built-in templates. Third, it starts with a good re-introduction paragraph at the top ("I’m sure you remember me from…").

King Innovation
This one has at least 7 images in it, but again, they’re balanced with a lot of text. Also, their HTML code is rock solid (we know, because they used our built-in template to make this). Yet another example of how you can’t just assume spammy keywords will get you blocked. This campaign has ALL CAPS, exclamation points, an iPod giveaway, and all kinds of stuff you’d normally think spam filters would hate. But somehow, the spam filters (including Postini) know it’s legit.

So I have no idea what the deal is with Postini. It’s very picky. The only common thread here is immaculate code, plus a good image-weight to text ratio.

Should You Care?
Is it worth spending a lot of your time trying to get through Postini? Depends on whether or not a significant portion of your recipients check their mail through a Postini server. One way you can tell is to open an old campaign’s stats, and dig into your bounce records (how to do that in MailChimp). Just eyeball your SMTP headers for any signs that a Postini server rejected you. Here’s an old article I found with an example Postini bounce. Or just CTRL+F and search the smtp headers for "postini."

According to Postini, they’re used by over 35,000 businesses. They seem to be used by medium to large corporations, and ISPs can become Postini resellers (they use it to offer anti-spam services to their customers). Check out their "Clients" page to get an idea of who uses them, and whether or not your list might consist of similar clients.