Mailbox Providers 101 – A five part series about the industry’s biggest email domains.

Here at SocketLabs we have customers ask us questions every day about the big mailbox providers.  These providers run a significant percentage of consumer inboxes and some also offer corporate and private domain mailbox solutions. Through the years of delivering billions of messages to these organizations, we’ve gained some great insight.  In the second part of this series we will delve into the Yahoo! Mail email gateway.

Yahoo has been offering mailbox services since 1997 and in its sixteen years of existence has accrued nearly 300 million active users (according to recent estimates).   SocketLabs answers many questions about Yahoo Mail because they have some unique anti-spam techniques employed to protect their users.

The most common concern of SocketLabs’ customers is in regards to delays and queue back-ups to addresses at Yahoo! Mail.  Yahoo commonly issues temporary SMTP errors to slow the rate of message delivery when certain thresholds are encountered.  These deferrals are in response to spam complaints, bad addresses, poor engagement rates, or even based on message content.  The deferral of a message does not mean that the final destination will not be the recipients inbox.  For example, we’ve seen transactional e-commerce receipts be deferred when a coupon code went viral and there was a quick change in message volume.

Beyond a standard message deferral, Yahoo may also permanently block what it deems a particularly poor source of messages.  The error code for that is: “421 4.7.1 [TS03] All messages from X.X.X.X will be permanently deferred; Retrying will NOT succeed.”

Another possible reason for message rejection at Yahoo! Mail’s SMTP gateway is a blacklisting by Spamhaus.  Yahoo’s use of this blacklist makes Spamhaus one of the most influential anti-spam organizations in the world.  The good news is that the SocketLabs’ suppression list feature helps protect against blacklistings from Spamhaus.

Following best practices will not only keep you off of blacklists, but it could allow you to be whitelisted with Yahoo! Mail.  Senders with good reputations can submit a request for whitelisting to help prevent any possible issues from arising.  Yahoo also honors Return Path’s Sender Score certification which helps achieve the best inbox placement rates possible at Yahoo! Mail.

Yahoo was once well known for its development of the Domain Keys authentication technology.  Domain Keys has now become DKIM and this authentication mechanism carries a heavy weight with the Yahoo! Mail platform. All SocketLabs’ customers have their mail automatically DKIM signed, and customers on Bronze and above service plans can customize their signatures with their own domains.

Adding DKIM signatures to all messages processing through our network not only improves message delivery rates, but it allows us to collect Feedback Loops (FBLs) in return.  FBLs are more commonly referred to as user complaints.  These notifications are generated when a user marks an email message as SPAM in a supported email client.  SocketLabs collects more FBLs from Yahoo than any other mailbox provider.  These complaining address are automatically added to a server’s suppression list to prevent further delivery attempts. This allows senders on our networks to maintain a positive reputation with Yahoo.

Check back soon for Part 3 of our Mailbox Providers series, where we will be looking at AOL’s email service!