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What sender score and IP reputation is really worth to your mail server

Posted on Feb 19, 2010 by Paul White

Most webmasters and server admins are relatively clueless as to whatmakes email really run.  Recently I was forced to migrate all mywebsites to new IPs.  I knew I was going to take a hit for this but Ididn't realize how much.  This whole experience have given me a newperspective on how to get into yahoo's inbox with your bulk emails andnewsletters.

History of my Mail Server

First as of a week ago everything was great on my mail server.  One of my bigger clients has a maillist of about 7000 people ( all double opt in ).  We were able to track the open rates of about 1000 emails every time we did a blast out.  ( once a week ).  Its taken years to figure out exactly what Yahoo, AOL, MSN, Gmail, and others want in order to let you into people's inbox.  To put it simple you can't buy your way into people's inbox.  It takes about 3 months of establishing your mail server's IP as a legitimate no spam mail server before they will start routing the majority of mail into the inbox.

How do you get into the inbox?

If you want to get into the inbox I suggest you use every technology available to legitimize your mail server.  This means have the IP of your mail server setup with an Reverse DNS that points to the hostname of your mail server.  So if your mail server normally is called mail.mydomain.com.  Have your ISP configure the IP's RDNS to point back to mail.mydomain.com.  Next you need to setup an SPF record to protect your domain's reputation.  Then if your mail server supports it, you need to setup DomainKeys and DKIM.  These are two technologies that allow receiving mail servers to authenticate the messages as being sent from your server.  If your mail server doesn't support it, I highly suggest you consider upgrading to SmarterMail 6.x.  Now even after you have setup all these technologies, there is one more thing that most mail servers use to validate you.  The first is your IP reputation, the second is your senderscore.  ( look it up at senderscore.org ).  The problem with both of these is you can't buy them.  The senderscore informs ISPs of both your reputation and the volume of email you normally send.  So if your mail server sends a high volume of mail and maintains a very high senderscore, you are likely to get into the inbox at yahoo.  But if you have a high sender score, yet normally you have a very low email volume the ISPs will use this information to determine that your mail server is doing something out of ordinary and therefore it may not be valid.  Senderscores have nothing to do with domains.  They are tied to your IP.  If your IP has been doing bulk mail for 6 months and has a very low complaint rate ( people marking the email as spam ), then you are likely to get most of the messages into people's inboxes.  But if your list is dirty with lots of bounce backs, this will hurt your IP reputation and will lower the bar for what the receiving ISPs will accept from your mail server.

The difference between a public IP block and a private IP block

First let me explain my hosting situation.  I own my own server , and I colocate it with Acronoc ( downtown Houston ).  I am running about 20 websites on this box.  Each website has its own IP address.  But these IPs were assigned from a public Class C block.  Meaning one customer might have x.x.x.1-.5 and another would get the .6-.9 and another .10-.14 and so forth.  This overlap in IP ranges meant that Acronoc was not able to setup a reverse WhoIs that would show ownership of one customer to a block of IPs.  A Class C block is also called a /24 block (which consists of 256 IPs).  A /25 block would then be 128 IPs.  A /26 block is 64 IPs, and so forth.  Now when you are using a shared block of IPs, you are at the mercy of your neighbors.  If one of them decides to send spam from his box, this could result in a blacklisting of not just his IPs but the entire Class C block ( 256 IPs ).  This is basically what happened to me a couple days ago.  Another server in the same Class C IP block as me,  was spamming.  Eventually it caught up with him, and Spamhaus ( the biggest and baddest blacklist in the world ) blacklisted our Class C IP.

What happens when your Class C is blacklisted by Spamhaus

In our case it was the Spamhaus SBL list.  Your ISP needs to kick the offending spammer, then contact spamhaus with information that the situation has been taken care of.  But Spamhaus might not instantly remove you.  In my case 48 hours went by and they still had not cleared our Class C IP block from their blacklist.  Something to understand is Spamhaus is used by every major ISP as part of their RBL checks.  This means your server will be rejected by yahoo, hotmail, AOL, AT&T, and many others.  Essentially make your mail server worthless.  Your clients call complaining about not being able to send mail.  You tell them you are working to get the problem resolved.   Finally I couldn't wait any longer.  Acronoc was good enough to give me my own Class C IP block so I would never have to deal with this again.  Actually they gave me my own /26 ( 64 IPs ) and will hold the remaining 192 IPs in reserve for me in the distant future.

Starting from scratch with your own Class C IP block

Now that I have my own Class C ( actually /26 ), and I have updated all my client's DNS entries to point to the new IPs, you might think everything would be back to normal.  But the truth is you just gave up a blacklisted IP for an IP that has no reputation.  Think of it like your credit score.  No credit score is just a little better than a bad credit score.  Now I realize that I can''t expect to get the kind of open rates I had with my old IPs.  But what I didn't realize was how much an IP with a good reputation is worth.

Within the first 24 hours.  Many of my clients were getting bounce back messages from AOL, saying come back later.  Basically many of the ISPs don't trust my IP since its new.  This is when just doing normal emails.  We haven't even started sending newsletters yet.  Its obvious that spam from unknown IPs is so bad, that with major ISPs you are guilty until proven innocent. 

The first thing you need to do is ensure everything is setup properly.  This includes RDNS on the IPs, and any domain text records ( Domain Keys, DKIM, SPF ).  Next once you have this done,  you need to resubscribe to the Feedback Loops.  For the ISPs that have whitelists you will need to reapply.

The importance of Sender Score

Senderscore which is used by most major ISPs is a value between 0 and 100 that shows the ISPs your reputation.  Unfortunately it takes 30 - 90 days until your senderscore will have a value other than N/A or 0.  This means you have to wait.  In the mean time many Feedback Loops won't allow you to join until you have a senderscore over 60.

Open rates on a new IP

For my client with 7000+ subscribers, our open rates have dropped from 1000 to 450.  This will increase once our senderscore comes back up.


If you find your mail server on a bad IP.  Try to get your own IP block /24 /25 /26.  Of course if you are with a shared hosting company, or have a dedicated server with godaddy where you are forced to use their mail relay, you can forget about this.  Usually the only way to get this is to buy your own server, and colocate it. 

Update 2/22/2010
This morning I checked on senderscore.org to see if anything has changed.  Before senderscore.org said there wasn't enough data to display a score.  Now its showing a score of 50.  Its good to know that the senderscore system updates relatively fast.  So within 5 days of moving to a new IP I got a sender score again.  I checked some of my other websites and they still don't have a score yet.  Though these sites don't do any bulk emails.  Even though 50 is much lower than the 95 I once enjoyed, I am sure with time my score will reach 95 again.  Once my sender score gets above 60 I can reapply to the comcast Feedback Loop. 

Update 2/27/2010
This evening I did another check to see if our senderscore has changed at all.  Sender Score was now a 70.  This means I can now submit my domain to all the Major ISP's feedback Loops.  This value will slowly get higher over time.  I also did a blacklist check and my IP is clean.  Even though the open rates from the domain in question is still not what it used to be, they are getting better with each send.

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Andrew Bonar | Aug 4, 2010 7:56 PM
You have written a great article their Paul, and its great to hear it from a personal user perspective.

Best of luck with improving your email deliverability and I am sure your reputation will improve over time.

Sender Score is important but there are some other major email reputation tools you may want to also keep an eye on, a quick free tool is available here: http://reputation-score.com
Leonardo | Jul 9, 2013 3:42 PM
Hello Paul,
Thanks for this article. I was verry worried about my brand new server and IPs and you calm me.
Im having this problem. Can you give me some tips to increase my reputation?
Paul | Jul 9, 2013 3:57 PM
Run spam checks on all outgoing emails sent.  This is a feature built into smartermail.  If any account is compromised move quickly to delete any remaining spam in the que, then throttle the account to something like 10 messages per hour.  

signup all your IPs on the feedback loops with the major ISPs.
Leonardo | Jul 9, 2013 4:34 PM
Hello Paul,
SmarterMail is a webmail software? Iv been reading and i understood that is like Zimbra am i right? I can install under linux?
Paul | Jul 9, 2013 5:16 PM
Smartermail is mail server software.  
You can learn more about it form the SmarterTools.com website.
It only runs on windows.  I highly recommend it.  Full of features that really help to cut down the spam.  
Leonardo | Jul 12, 2013 12:59 PM
Nice Paul! Thanks, i will check it out.
I saw your email reputation and its very high! Congratulations!
For my server im running Interspire Email Marketer, i enabled the RDNS, im subscribing to the Feedback Loops including Hotmail, Yahoo etc.
Wich Email Marketing Software do you use?
Do you thing i can start mailing now? Even if the open rates will be very, very low?
Paul | Jul 12, 2013 1:07 PM
My Mail server is running SmarterMail 11.x.  As for the email marketing software, I custom developed my own system.  Make sure you are signed up with all the major FBLs, before blasting.  Take it slow.  Blast small batches at first. Maybe only 500 in 24 hours.  Only send to people that opt in to your maillist, and move quickly to remove bad emails from your list.

If you move to fast, most of your emails will not make it to the inbox, and may ISPs will blacklist your IP.  
Leonardo | Nov 30, 2015 2:32 PM

Hey Paul!

2+ years later and i still need to thank you for your tips. They were very helpful!

I got a 99 grade from Senderscore and Outlook accepts all of my messages.

I just got a new IP block and I remembered your precious article. Will do it again!




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