Why does SMTP host IP get blacklisted and how to prevent it?

Email verifier pro script doesn’t provide any guarantee that your host IP will not receive any blacklist. As you will be sending bulk SMTP requests to random external servers through smtp response. Even though Email Verifier Pro does not send any actual email or any data to third-party email addresses mailbox as it uses our own custom rules and filtering from script but their mail server strict anti-spam filtering may not allow you to spy on them which may lead to blacklisting. But we will explain here how it happens and how it can be prevented may not be fully but partially. But do remember, Email Verifier Pro is working everyday in improving its system architecture, we will provide more facilities to users for reducing their blacklist issues and staying more controlled with data response to fight against a blacklist. However, preventing a blacklist is user’s sole responsibility.

Why does it happen?

Being blacklisted is triggered by a variety of set criteria. For example, if a certain amount of spam traps are hit or suspected SMTP spam is received from a particular email/IP address within a certain time frame, an email provider like Google or Hotmail will realize the IP address it comes from. In response to this, they’ll blacklist the IP address and any email sent from it will bounce back. This most often happens when this trigger on SMTP server which is protected over a firewall and tight anti-spam security system. There are quite a several we can mention like google, Hotmail, Yahoo, Mimecast, Comcast etc. Because of it for some well popular mail servers, we are not using SMTP connection for a check rather using 100% safe procedure. It already works on Hotmail, yahoo and aol servers.

As technology is getting updated so are spam securities getting improved. Nobody likes to receive a high amount of unauthorized SMTP connections to be getting hit at their system end. Nobody wants their customer information to be getting leaked. Which why every host out there follows a different pattern to prevent this from happening and reports any abuse.

When a HOST IP doesn’t have a proper rDNS PTR record set and no DKIM / SPF set at the host system for FQDN then it leads to an improper SMTP configuration. When you use an Improper SMTP configuration to connect to another host machine, denies your request to communicate and blocks your IP and reports it Spam Database List.

Also, this blacklist usually gets impacted on new IP address heavily. Suppose you just got a server and you plan to use it for sending bulk SMTP connections over another server to collect a user address from their mailbox. But that server has this tight spam security system to check by understanding as you are making random email address request to check at their system end containing their domain name. When this email address actually doesn’t exist and your system keeps on doing that, they straightly send your IP and report it to DNSBL’s – Domain Name System Blacklist service providers. Spam security starts getting monitored more strictly on new host IP once they get a single blacklist. Once a new IP gets blacklisted its IP reputation comes into a stake. To regain that reputation value again and reduce this strict monitoring, there are several things that can be followed which will be given in How to Prevent It.

How to prevent it?

We do not guarantee that this may completely help you control not being added to blacklist host IP as it’s not in our hands. But following this may reduce your Host IP chance of being blacklisted and may not be on blacklist at all.

1. As a first step set up your IP and Domain name to any free blacklist monitoring system to get notified whenever your host IP and Domain name have been blacklisted so you know you have to work on it!
2. Make sure your SMTP mail server setup passes mail-tester.com check approx 10/10.
3. A new domain must wait for 7 to 14 days or depending on the recommendation time on mail-tester.com or any DNSBL server waiting period before using any bulk or spam process.
4. SMTP server using FQDN address. eg: mail.yourdomain.com, vps.yourdomain.com, yourdomain.com
5. Hostname should contain the same rDNS PTR record domain and point to the same IP.
6. SMTP server port 25 opens and can communicate through it to the third-party SMTP server.
7. Server using proper DKIM, SPF, rDNS and PTR record setup.
8. Try warming up your new SMTP Server IP. If you are using a new host with IP then use a low amount of bulk scan limit for SMTP connections to gain trust on DNSBL’s network. eg: 100 a day, then 1000 a week, then 100k a month, then 100k a day from lower to higher. Older IP with a good reputation has more chances of rarely having blacklist and getting quickest delist if requested on specified DNSBL system. But if you keep spam without fixing IP reputation and backlist then they will quickly put the host IP on the list again. DNSBL’s network doesn’t go easy with newcomers. So, if you get host IP first-time blacklisted then always go slow and don’t push for a stress test because they have their eyes on your host system IP. You can always ask your VPS provider to replace your VPS host IP for a small fee and reconfigure new IP on all existing DNS records IP address.
9. Make sure you don’t run multiple email verifier pro instances from a single VPS. Always use the latest version of email verifier pro contains important feature updates.
10. Don’t use fake emails, public domain emails or SMTP configuration on the system scan settings.