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Maintaining Deliverability With The ‘Big 4’

What’s the magic pass/fail standard that decides whether your email reaches a recipient’s inbox or their spam folder…or even gets delivered at all? Sender Reputation, determined by a bevy of metrics and measures that include authentication via SPF, DKIM and DMARC protocols, complaint rates, the number of spam traps hit, bounce rates and, ultimately, user engagement metrics: if you’re badged spam by the addressee, it’s a rough road back to the inbox.

But your Sender Reputation – and, therefore, your deliverability — may not be the same across the ‘Big 4’ major inbox providers.  Yahoo, Gmail, AOL and Hotmail don’t share their data with each other.  They also vary in how they implement authentication protocols, user engagement metrics and other practices.

So it’s obviously useful to understand how each of them gatekeeps deliverability.  Here’s a rundown of some of the key considerations about each, condensed from An Email Delivery Report for 2013: Yahoo, Gmail, Hotmail & AOL, as researched by EmailDirect, a small Sacramento, CA ESP:

Yahoo!

  • Yahoo! checks for SPF, DKIM and DMARC flags.
  • SpamGuard, their proprietary filter, learns to flag spam via user complaints and lack of engagement.
  • Yahoo! maintains a whitelist, but it doesn’t ensure delivery, since all senders are still subject to SpamGuard.
  • Good reputation metrics and getting subscribers to put you on their “safe” lists will protect your deliverability.
  • Yahoo! references block lists at The Spamhaus Project – so being listed there will result in a block.

AOL

  • DKIM authentication is needed with AOL.
  • AOL uses an IP-based whitelist; mailers with good reputation scores in the AOL Feed Back Loop program qualify for it.
  • Their spam filter is proprietary and custom-built, influenced by metrics like complaints, unknown users, content, bounce processing and spam traps.
  • AOL references the block lists maintained at The Spamhaus Project.
  • If you’ve been routed as junk mail or bounced, good luck!  Getting back into the Inbox is tough, though a form to request delisting from AOL’s internal block list is available.

Gmail

  • Unlike other inbox providers on this list, Gmail doesn’t employ a feedback loop or whitelist.
  • They’re very aggressive in blocking bulk commercial email compared to the other major inbox providers.
  • Poorly-optimized creative content can prompt junk mail routing.
  • Once you’re sent to the junk folder, it’s hard to get back to the Inbox.  Requests to be removed from Gmail’s internal block list can take several months – or longer.

Hotmail

  • Microsoft releases more reputation data than these other inbox providers via its Smart Network Data Services (SNDS) program.
  • Windows Live Hotmail has switched to SPF authentication.
  • They filter email using Symantec/Brightmail Probe Network and Smartscreen filtering, along with proprietary content-level filtering.
  • Blocking may result from being listed with Brightmail; removing blocks requires contacting Symantec, not Hotmail.

Looking for more information about email best practices that can get you into the inbox? Download our free eBook, Email Best Practices 101.

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