[SOLVED] Unfortunately, messages weren’t sent. Please contact your Internet service provider…

S3140 block list and how to solve it. So relax there is a solution to you problem.  It is amazing to know that the first electronic spam mail was sent in 1978 as an advertising email to over  350  recipients on ARPANET, composed by Gary Thuerk. More than 80% of emails sent these days are spam even tho 1 in 12 million will end up achieving a sale, with such a crazy low conversion they still keep doing it. 

Email providers like Gmail, Yahoo mail, Outlook…are trying hard to fight spammer by providing tools to their members to block email addresses or even an entire domain and as you know domain names are associated to a DNS ( ip addresses ) and that is where it start to be tricky. Because your ip you just inherited from your hosting provider may be one of them or you wouldn’t be reading this. 

There is however a solution if your server is using one of the blocked ip addresses. I don’t know who is rejecting your emails but in my case it was Microsoft Outlook/hotmail/Live email service. When i looked to my member’s database i noticed that i had a big number of new users with non-verified email addresses and the common thing about all these members is that they are all using Microsoft email service like outlook, hotmail… live. Long story short I found out that my server ip address was blocked by Microsoft even before i got it with my dedicated server.  So to make sure of it i sent an email from my domain to my wife’s hotmail account as a test, here is the replay I was getting 


Recipient: [SMTP:i changed this as an example@hotmail.com]
Reason: 550 5.7.1 Unfortunately, messages from [xx.xxx.xxx.xx] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider  


I started looking and searching about S3140 block list  and how I can get hold of someone from Microsoft to solve this issue. Finally ( and to save you time ) I found a form that is provided by Microsoft where you can submit a request to clear your ip addresses. Sender Information for Outlook.com Delivery  <– Click there

i took my time and filled up and sent  the above form  and after 24 hours and i received an email from the support team at Microsoft with the following

Conditionally mitigated
xx.xxx.xxx.xx; xx.xxx.xxx.xx
Our investigation has determined that the above IP(s) qualify for conditional mitigation. These IP(s) have been unblocked, but may be subject to low daily email limits until they have established a good reputation.
Please note that mitigating this issue does not guarantee that your email will be delivered to a user’s inbox.
Ongoing complaints from users will result in removal of the mitigation.
Mitigation may take 24 – 48 hours to replicate completely throughout our system.

I waited couple more days to make sure the mitigation takes effect then i  resent email verifications to all my non-active members that never received it the first time because of the block,  and it worked without a single bounce back or problems. 

So if you have an ip address that is blocked by outlook and you receive an error like block list (S3140) try the above process and Let me know if this helped you!  or just share this in twitterer facebook to help others!