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How to increase your open rates for your bulk emails

Posted on Nov 14, 2009 by Paul White

If you are are like me you have a strong belief that if you want itdone right you have to do it yourself.  Running a Mail Server thatsends any kind of bulk emails brings many issues that noobie ServerAdmins don't have a clue about.  I found there wasn't much informationabout how to properly run a mail server so I thought I would write acomplete blog on the issue.

The major Mail Servers ( Yahoo, AOL, GMail, Hotmail ) more than likely account for 90% of your maillist.  It doesn't matter if you have an double opt in maillist, or you some how aquired it.  The fact is most of the emails will be Yahoo, then Gmail, then Hotmail and finally AOL.  For this reason your first objective is to make these 4 guys happy.

Step 1 to increasing your open rates, Close the Relay

Make sure your Mail Server is not acting as an open relay.  Even today there are still quite a few mail servers that will relay anything thrown at them.  Spammers and hackers will find these boxes and use them to blast their Spam.  If your box is an open relay, it may get onto an RBL list of known Open Relays and any mail sent from it could be blocked.  To check your server and make sure its not an open relay go here

Step 2 to increasing your open rates, Reverse DNS

Make sure the IP your mail server uses has an Reverse DNS entry.  You will need to contact who ever controls the network that gave you your IP, or your ISP.  Your RDNS should be changed to your domain, or the hostname of your mail server.  Example if your mail server is "mail.mydomain.com".  Have your RDNS changed to "mail.mydomain.com".  Many mail servers block connections from email sent from servers that lack an RDNS.  To check your RDNS, goto this site

Step 3 to increasing your open rates, SPF Record

An SPF record stores information about what mail servers and IPs are authorized to send mail on your behalf.  This is something you setup in your DNS records. To check your SPF record goto this site
For more information on how to properly setup an SPF record, and how it works goto this site

Step 4 to increasing your open rates, Domain Keys and DKIM

Domain keys and DKIM are not supported by all mail server software, however Yahoo does check for them, so if you can setup them up I highly recommend it.  Domain keys adds a special header to your emails that gives the receiving mail server the ability to check to see if the email is legitimate.  Logically these keys are like a digital signature.  If you need a mail server that supports these I highly recommend SmarterMail 6.1.  Its an easy to use and easy to setup mail server software, and it supports both Domainkeys and DKIM.  These are so important I highly recommend you upgrade your mail server software to the latest version of SmarterMail if your current mail server software doesn't support them.  There are also addons for older versions of SmarterMail, but I highly recommend you stay aware from them.  These addons startup a process for each email sent to generate the DomainKey signature.  This will spike memory usage, and could potentially crash your server.  I personally crashed many VPS systems using this addon feature.  SmarterMail 6, is very conservative on memory usage, and fast.  To test your DNS to see if you have domain keys setup goto this site
Another site that will help you test to make sure your emails are signed with domainkeys is

Step 5 to increasing your open rates, Lower your send rate

Mail mail servers have the option to set how many threads can run at once.  I found that if you have emails coming off your server too fast this tends to over welm yahoo, and they might temporarily block your IP.  I have my mail server set to only use 10 threads at once.  Some mail servers use the frequency of emails from a single IP as a way of detecting bulk emails.  They will then direct this email into the user's spam / bulk folder.  I have found that slowing down the rate in which emails come off your server will help to increase the number that make it to the inbox rather than the bulk / spam folder.

Step 6 to increasing your open rates, use the Feedback Loop

A Feedback Loop is something I recently discovered.  Each of the major Mail Servers has a Feedback loop system that you can apply to.  Even though we all provide unsubscribe links at the bottom of your emails, many users don't trust the unsubscribe links.  Instead they will simply click the SPAM button on Yahoo.  This of course is a hit against your IP, and domain.  By subscribing to the Feedback loop, anytime a person clicks the SPAM button, Yahoo will forward the message that you sent them.  This enables you to manually remove them from your lists.  The only ISP that doesn't support the Feedback Loop is Gmail ( as of this posting ).  The rest of them do have a Feedback loop program you can join.

Here is a list of ISPs and links to their Feedback Loop System.
I have ordered them in order of importance

Yahoo! Feedback Loop Form

AOL Feedback Loop 

MSN/Hotmail Feedback Loop

Comcast Feedback Loop

Excite / Bluetie Feedback Loop

NetZero/Juno Feedback Loop

Road Runner Feedback Loop

USA.net Feedback Loop

Check your Sender Score

Sender Score which can be found at senderscore.org is a system that helps ISPs determine your IP reputation.  Many major ISPs use senderscore, and contribute their spam data into the system.  Since Spam usually comes from IPs that have no prior email reputation ( zombie systems ), or are virgin IPs recently assigned to a new website, using the sender score can help determine if the IP has a good reputation.   The Sender Score is a number from 0 - 100.  Its a percentile score.  Some of my larger sites have sender scores of 95 and 96.  This makes a huge difference in your open rates. Especially getting into Yahoo's Inbox.

Comcast specifically uses a sender score to determine if they will allow you to join their Feedback Loop. On their website they state In order to subscribe to Comcast's Feedback Loop, you must be the party responsible for a server that sends mail to Comcast customers.  If you are the owner of a service hosted on a shared mail server, it is recommended that you have the server owner contact us to sign up.  In addition, requests will be approved based on the following criteria:

  • IPs with a SenderScore of 60 or above will be accepted.
  • IPs with a SenderScore of 30 to 60 cannot appear on any DNSBLs.
  • IP with a SenderScore below 30 will not be approved.
All denials will be returned with an explanation of why and remediation steps. Applicants can reapply at any time.

There is a 7-14 day window for approvals.I checked one of my clients and they had a score of 25 and were not eligible for feedback loop with comcast yet.  Another client was 95.  Some others didn't even have a score.  I highly recommend you check your mail server's IP with senderscore to see how it ranks.  I suspect some ISPs will start to use this to determine how it routes your email into the inbox vs the bulk folder.

Step 7 to increasing your open rates, get your own IP

This means your domain's mail server should have its own IP address that is not shared with any other domain's mail server.  The latest SmarterMail 6, Supports separate IPs and HostNames per Domain. 

Step 8 to increasing your open rates, patience and time.

You must understand that the major Mail Servers will use your IP's sending reputation in order to determine how it should handle email you send. The results are this
Good sending reputation - Emails go to Inbox
Ok sending reputation - Emails go to Inbox with some going to Spam Folder
Questionable reputation - Eamils go to Spam folder mostly, you may also be temporarily blocked
Bad reputation - Your Mail Server's IP is black listed perminently, usually for 6 months before you can apply to be allowed again.

Step 9 to increasing your open rates, check the blacklists

If your open rates are very low, you may have found your way onto a RBL ( real time black list )
check your IP's status here


If you have done all of these, and are still getting low open rates, just give it time.  Understand that you will never get 100% open rates.  Simply because many Email clients will block your beacon images that you use to track if your email has been opened.  Its also important to know what open rates you should expect.  Anything around 16% would be very good.  This is assuming you have a maillist in the 5K+ range.  Smaller lists may have a higher open rate.  However it may take months of sending bulk emails with no complaints before you will start to see open rates like this.  Ultimately Mail Servers have no problem with Bulk Emails if they are solicited.  Its very important to keep a clean list.  If you have bounces make sure you clean them off your list and fast.

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Leonardo Lauretti | Aug 15, 2013 9:49 PM
Nice post! Following your tips i got a 99 sender score.
Thanks a lot!
I would like to know if you can make a post about your Email Marketing System with some screenshots or even the code if you dont mind.
Thanks a lot!

Paul | Aug 15, 2013 11:23 PM
The code I wrote for handling email blasts is not modular in way that would allow me to easily just copy paste it.  Even if I did, there are dozens of helper functions that you would need to see to fully understand what is going on.  If I get the time I might post some example code, but with my current work load its not going to happen any time soon.
Thanks for the feedback though!
Leonardo Lauretti | Aug 16, 2013 2:47 PM
Thanks for the reply, Paul!
The company i work was using Interspire Email Marketing.
The software is very expensive so to cut out the expenses we just decided to stop using the IEM, now im using the PHPList but is i think it could be better.
My idea is to start the development of a "in house" mailing system.
The only problem right now is to automatically handle the bounces and auto unsubscribe.
Paul, can you recommend me a good timing to send the emails to dont get into any RBL?
Thanks a lot! (Sorry for my english, im Brazilian. : )
Paul | Aug 16, 2013 3:11 PM
Every mail server is different in the kind of volume they are going to accept. It all depends on what kind of email volume your mail server normally does when not blasting.  I have one client that blasts to about 15K emails and we have no problem getting them out in 6 hours.  But this client also is running a social network which results in thousands of daily notification emails.  Since their average daily volume is high, pushing out a bunch of emails is not a problem.  If your mail server sits idle most of the time, and you are trying to blast, you will have problems.    I would recommend trying to let them gradually let them trickle out.  Maybe only 100 per hour, til you get your volume up then start to gradually increase it.  Eventually you will hit a point where some ISP will start to kick back your messages, at which point you should pull back a little.  

As for unsubscribe requests. I include a single opt out removal link at the bottom of all my emails.  For the people that get the message and hit spam ( which results in the FBL notifying me ), I will open the message and hit the removal link myself.

Bounce removal can be tricky
I actually wrote my own script to handle that.
I typically clean my lists once every 2 - 3 weeks.  If you are a high volume operation I would even recommend cleaning your lists daily.  Most of my clients only blast maybe once or twice a week, so in my case there is no rush to remove the bad emails.

My script uses a C# POP3 class to login to the email address that received the bounces, and read each bounce message.
It looks for specific words that indicate the type of bounce message.
Example I might search for "out of the office"  which is a common autoresponder people setup.  Then the script will just delete the message.  It also looks for 4xx which means delayed, and 5xx which means hard bounce.  You have to be careful though example. 57x typically means their spam filter kicked it back.  

Since everymail server typically replies with their own custom bounce messages you end up figuring out the patterns from each server, and writting server specific code to determine the bounce type.  After I run the script I have pretty much eliminated 80% of the bounces, then I manually go through and sort and handle the remaining messages from there.

I applaud you doing this yourself in house.
If you want it done right you have to do it yourself.

Leonardo Lauretti | Aug 16, 2013 6:26 PM
Nice, Paul!
I will add a reply-to on the email headers to an address like bounce@mydomain.tdl.
Then try to open the mail inbox via PHP and handle the messages by the subject.
If its a hard bounce it will just delete the user in the MySQL.
Do you think that doing it online via PHP is a good choice?
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