How to Resolve Common Deliverability Challenges

More than 80% of all delivery issues arise because of a problem with your sending reputation.  Your sending reputation is based upon your sending patterns and volumes, mailing infrastructure, list hygiene (spam traps and unknown users), and subscriber complaints. Recently we gathered a bunch of data to figure out why our email was being blocked. Today, let's look at how we can resolve the reputation issues and get our email back to the inbox, based on the data we gathered.

1.    If the problem is complaints:  Too many complaints leads to blocks.  Everyone knows this. And the easy answer is, "send better emails." But just making changes blindly is not going to help much.  In fact, it might hurt you if the changes you make satisfy one group of subscribers but in turn annoy another group.  You need to figure out, with some real precision, where your complaints are coming from so you can fix the problem surgically.  By doing an analysis on your complaint file you can see if there's a correlation between high complaints and permission level, data, source, mailing frequency, content type, vintage, or demographics.  Once you've identified a probable cause (or, in some cases, causes), you can do some testing until you find the right solution that causes your complaints to decrease.



2.   If the problem is too many unknown users: If you see that your unknown user rate is above 5%, there's a high probability that your delivery issues are a result of this.  The first thing you should check is to see that your system is still processing bounces.  Your IT department can verify this and can quickly correct. 

Another common reason for a high unknown user rate includes acquiring addresses from a third-party source with less than stellar acquisition and verification practices.  And I'm not just talking about co-registration, append, and list rental, though those do tend to be the most likely culprits.  But we've seen clients with unknown user issues caused by address book uploads and offline acquisition.

Depending on how bad the issue, is you have a few options.  You can either mail these addresses a welcome message from an IP that is separate from your regular mailings, use a third-party list hygiene service to clean the list before mailing, or stop using that data source.  No matter what the data source, any address that hasn't been mailed in awhile -- generally anything older than three to six months -- needs to be suppressed. People abandon email addresses often and infrequently emailed addresses are often a source of a high unknown-user rate.

3.   If the problem is spam traps:  Like unknown users, spam traps are a result of poor list hygiene methods.  By applying most checks above for unknown users, you can prevent ever acquiring a spam trap.  You can also implement a double opt-in process, as a spam trap can never confirm a confirmation message.  If that's not an option, send a welcome message from a dedicated IP address and quarantine your data if a spam trap is discovered.  Senders should also implement a win-back and reactivation strategy when no response is seen from an address after three to six months. 

 If you already have a spam trap on your list and re-permissioning your entire inactive file isn't an option, then your choices are more limited and difficult.  Finding and removing spam traps is usually a long and tedious process of elimination.  You will need to systematically segment and re-permission slices of your list until it is clean. 

4.   If the problem is poor infrastructure: We've found this to be an infrequent problem. The great news is that infrastructure issues tend to be the easiest to solve and the resolution of the block is very quick.  The most common delivery issue dealing with infrastructure is connection and throughput settings.  Each ISP has its own unique settings based on the capacity of its systems.  Having too many connections or sending too many messages can cause ISPs to temporarily block you, or can overload their system and return a "too busy, try again later" message. 

The second most common issues are an absent or improperly configured reverse DNS for the sending IP addresses that's not a Fully Qualified Domain Name (FQDN), or not having an MX record.  Even though it rarely happens today, test your infrastructure for vulnerabilities for open relays, open proxies, or backscatter  These are security issue that can cause you to get blocked or blacklisted and can also cause high unknown users and spam trap hits.  If you find this is the cause, work on your IT staff to review your MTA documentation on how to correct these issues.

5.  If the problem is content:  While it's most likely that your blocking issues are due to a reputation factor, content can be a cause as well. The process of fixing a content issue is similar to fixing complaints and spam traps.  You need to segment and test in an iterative process until you eliminate the elements that cause your email to be filtered. 

What about blacklists?  The good and bad news about blacklists is that they are infrequently the cause of blocking.  A very few blacklists are used by large, commercial ISPs.  But being on a blacklist is bad news because it indicates that you have a reputation issue (or, less commonly, a content issue) that will lead to blocking.  Fix the reputation issue and you will most likely be removed from the blacklist, but more importantly you will start seeing your email delivered to the inbox.

Many marketers are frustrated that blocks can't be resolved by simply picking up the phone and calling the "guy" at  But I think this is actually really great news. You aren't beholden to anyone else and you don't need to convince anyone to deliver your messages.  You have the power to ensure that your messages make it to the inboxes as intended.

Of course there are a few instances where a call to the ISP is warranted.  In my column next month we'll discuss what those instances are and, more importantly, how to contact them for the best and fastest resolution.

(Huge thanks to my colleague Tom Sather, Director of Professional Services, who assisted with this column and shared a lot of great information based on his work with hundreds of clients.)

1 comment about "How to Resolve Common Deliverability Challenges".
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  1. Bill Kaplan from FreshAddress, Inc., October 11, 2010 at 3:19 p.m.

    Good bird's eye view of deliverability challenges, George. Given that almost all deliverability issues stem from problems with the underlying list (spam complaints, unknown users, spamtraps), companies need to be more proactive about keeping their email lists clean from the point of registration and forward.

    Real-time or batch email hygiene and correction services should be utilized to keep problem data from getting into your marketing database from the start. Whether your customers are opting in online or being delivered to you through co-registrations or some third party process, don't add email addresses into your database until you've checked them. This will help minimize bounces, spam complaints, and spam traps due to either inadvertent keystroking errors as well as sloppy, unscrupulous, or malicious registrations.

    As for dealing with the 30% annual attrition rate in email addresses, watch your bounce processing carefully and be aggressive in pulling out unknown users. Better to err on the conservative side here rather than run the risk of getting blacklisted and possibly bringing down your entire email program.

    Finally, companies should clean their working lists once or twice per year to catch small problems before they become larger ones. The majority of spamtrap addresses are former working email addresses whose domains have since been closed, in which case you might never receive an "unknown user" error as there's no one on the other end sending back a bounce reply. Accordingly, one needs to be careful not to keep messaging these because they might just be landing in Spamhaus's inboxes.

    Deliverability is critical to the performance of your email programs. Doing a little bit of work upfront and on an ongoing basis will help you maximize the significant returns available here for the taking.

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