by Ryan Ozawa
Article filed in
What is IP Warming?
by Ryan Ozawa
Unsolicited commercial email, also known as spam, has been a scourge of the Internet since the 1990s. In 2008, it accounted for more than 90 percent of all email traffic. While the percentage has actually dropped over recent years, more than 140 billion spam messages were sent in December 2020 alone.
Spam is such a pervasive and massive problem that complex and intricate countermeasures have been put in place to make it difficult to send large volumes of email. While this is good news for recipients, it does present barriers to organizations that have a need to send email messages to hundreds or thousands of people.
In order to be able to send email in large volumes, senders need to maintain a good sender reputation, which often involves warming new IPs before using them to send bulk email.
What is sender reputation?
Just as credit scores are used by financial institutions to determine whether someone is a low or high-risk customer, sender reputation scores tell ISPs and email providers whether they should deliver, or simply block, email messages coming from certain IPs.
To fight spam, global network services companies work with regional internet service providers (ISPs) to track where spam is coming from. The Talos Intelligence dashboard, provided by networking giant Cisco, shows these malicious senders in real-time. For example, it shows that computers in Russia, China, Turkey, and Belarus are each the source of more than five percent of total spam on a given day.
Each of these computers, identified by their Internet protocol (IP) address, is monitored and tracked over time. The IP addresses used by the most egregious spammers are flagged with a low sender reputation.
To make it even easier to identify bad senders, there are widely referenced blacklists that ISPs and email providers can use to automatically filter out likely spam messages.
What happens if a sender is added to a blacklist?
If an email sender, identified by its IP address, has a low sender reputation and is added to a blacklist, any messages it sends will not be delivered. While sometimes senders are notified that this has happened, usually there is no indication from the sender side that messages are being blocked. Senders might only be able to confirm that they are on a blacklist by looking up their IP addresses on published blacklists.
In the case where a single IP address is being used to send email from multiple people or organizations, such as in a shared webhosting environment, landing on a blacklist can impact everyone using the same server, even if only one user is sending spam.
Once an IP address has been assigned a poor sender reputation score and has been added to blacklists, it is extremely difficult for senders to recover. In fact, It is much easier to establish a positive reputation as a new sender than it is to repair a bad reputation.
Unfortunately, it’s easy for anyone, including spammers, to move to a new IP address. To avoid this, new IP addresses face their own restrictions.
What is IP warming?
An email sender using a new IP address, also known as a “cold” IP address, is not prevented from sending email, but it is watched closely for abusive activity.
The number of emails that can be safely sent from a cold IP address is much more limited than an established sender with a high sender reputation. In order to be able to send hundreds or thousands of emails, the new IP address needs to be “warmed up.”
IP warming is the process of gradually increasing the number of messages sent from a “cold” server until it has a high enough sender reputation to support sending emails in bulk. For example, sending only 20 email messages an hour on the first day, 60 email messages an hour after five days, and 300 emails an hour after a week. This process continues over time until the desired sender reputation is achieved.
In order to stop spam, ISPs and email providers check IP addresses for their sender reputation score. A poor sender reputation often lands senders on blacklists, and those senders lose the ability to send emails. Starting over with a new IP address is easier than rehabilitating a poor sender reputation, but requires time for IP warming.
How Paubox can help
Paubox takes extra care to maintain high sender reputation scores to ensure our customers’ HIPAA compliant emails are delivered directly to the inbox securely. The Paubox Email API can be leveraged by healthcare organizations to send test results and other protected health information (PHI) at scale, while protecting privacy.
With our HITRUST CSF certified product, patients receive encrypted emails directly to their inboxes—no passwords or portals required. Easy to implement with clear documentation, a developer’s experience is as seamless as the email recipient’s.