Ideally, your email list would be populated exclusively with email addresses of people who are actively engaged with your brand and want to receive your emails. Reality is often very different, but it’s important to strive for this ideal because the quality of your email list can have a tremendous impact on your deliverability.
Spam traps are email addresses that don’t belong to active users and are used to identify both spammers and senders with poor data quality practices. Mailbox providers, filtering companies and blacklist administrators create and manage spam trap networks to monitor email received at these addresses.
When a mailbox provider sees a sender hitting spam traps, they question the sender’s list quality, since spam trap hits indicate that the sender either:
- Acquired the email addresses through questionable means, or
- Is a legitimate entity with poor list hygiene.
They then place verdicts on the sender’s IP address, domain or content, allowing their partnering mailbox providers or filtering companies to take action such as placing a temporary (or even permanent) block on the sender’s email. The type and age of the spam trap often influences the tolerance a trap operator has, and the severity of verdicts placed on senders who hit spam traps.
Mailbox providers monitor the addresses to which you are sending and will filter or ultimately block your mail if poor list quality is identified. There are three types of data you want to monitor within your list: unknown users, spam traps and inactive subscribers. Subscriber complaints are also a strong indicator of poor sending practice, and are an important factor in filtering decisions, as we’ll explore below.
An unknown user is a recipient that never existed, has been terminated by the mailbox provider or was abandoned by the end user. Mailbox providers return a hard bounce code indicating when email is sent to an unknown user.
- 550 <firstname.lastname@example.org> User unknown
- 550 <email@example.com> Mailbox does not exist
- 550 <firstname.lastname@example.org> Invalid recipient
All unknown users should be removed from your file immediately via bounce processing.
An unknown user rate is calculated by dividing the count of email addresses associated with 5xxx unknown user bounce messages by the attempted volume of mail. Keep your unknown use rate below 2% to achieve high inbox placement. Unknown user rates exceeding 10% will likely cause deliverability issues.
3 Types of Spam Traps
Pristine spam trap
Also called “honey pots,” these addresses were set up solely to capture bad mailers and were never used by a live subscriber. Many spam trap operators will hide their spam trap email addresses on websites, so they are only visible to harvester robots. When senders harvest email addresses from websites, they gather pristine spam traps. Any email sent to these addresses is considered spam.
Typo spam trap
Essentially, these are email addresses with misspelled domains. Major ISPs control every spelling variation of their domain.
Recycled spam trap
These addresses once belonged to a real person but were converted to spam traps after being abandoned. Recycled traps identify legitimate senders with weak list hygiene and data quality practices.
How to Eliminate Unknown Users and Spam Traps
Quarantine new data until you send a welcome message and do not receive a 5xx unknown user bounce. This keeps you from adding bad addresses to your regular campaigns.
Email your list regularly. In general, the less often you send email, the more likely you are to see high bounce rates. Infrequently emailed lists are also more likely to harbor spam traps as old addresses may have been converted into trap addresses since your last campaign.
Provide easy update options. People often change email addresses and may be willing to update their contact information if you make it easy. Even if you don’t have a full preference center, offer change of address and frequency options at the point of unsubscribe.
Monitor subscriber activity. As a rule of thumb, a subscriber who has been inactive for more than a year and is not responsive to your re-engagement campaigns should be removed from your list. Implement shorter time periods of six months or even 90 days if you mail frequently or send third party advertising. But keep in mind that every sender is different—you should test to determine the strategy that works best for your business.
Consider double opt-in. Marketers who make customers take an action—usually clicking a link—to confirm their subscription generally have smaller lists than they would otherwise, but those lists are much cleaner than non-confirmed lists. They also tend to have lower complaint rates and better inbox placement rates.
Run basic list hygiene processes. Regularly clear out role accounts (email@example.com), obviously bogus addresses (firstname.lastname@example.org), and errors (email@example.com).
Select data sources carefully. Vet third party data sources and perform regular audits on the data they provide. Consider tracking data sources throughout the subscriber lifecycle, to make more informed decisions about third party data sources.
Inactive addresses represent customers on your list who have not opened, clicked or taken some kind of action for a significant amount of time. Most marketers have many inactive addresses on their list. For some, this segment can represent as much as 70-80% of their list.
Inactive subscribers are undesirable for many reasons. Not only could these addresses be a source of unknown users or spam traps, but they also bring down response rates for the entire program and negatively impact your overall reputation.
To best manage your email program, get a process in place to identify inactive subscribers.
Use campaign performance tracking data to analyze typical email response over time.
Track opens, click and bounces. Note when opens and clicks drop off and bounces rise. Use that data as a baseline for separating your active and inactive email addresses. After these groups have been identified, reduce the mailing frequency to inactive addresses.
Audit sources of inactive addresses. Review the sources of the inactive email addresses (e.g., online quote, affinity partner, referral, etc.) to determine any behavioral patterns tied to a particular source.
One of the main goals of mailbox providers is to protect their users. As such, they place a high degree of importance on their users’ feedback and preferences. If email recipients are complaining about your email, mailbox providers will perceive your email as unwanted and will block your mail from the inbox. As a result, complaints are among the most important contributors to a poor sender reputation.
There are three ways a subscriber can register a complaint:
- This is junk/spam button: The subscriber hits the junk or spam button (or equivalent) in their email client.
- Postmaster complaint: The subscriber sends a message complaining about a sender to the postmaster group at the mailbox provider.
- Filter application complaint: The subscriber sends a complaint to a filtering application or a complaint-driven blacklist.
Email recipients complain for many reasons but tracking down the source of your problem can take some effort. Here are a few suggestions:
- Review all your list acquisition sources to see whether any of them generate a disproportionate number of complaints. Take steps to clean up your list acquisition practices or remove the bad source(s) altogether. Paid lists, affiliates and peer-initiated web forms are common culprits.
- If subscribers don’t recognize your brand or remember signing up for your email program, they’re likely to complain. A well-executed and timely welcome message can bring subscribers into the fold, educate them about your brand, and reinforce the benefits of your email program.
- Content that’s not relevant or interesting to your subscribers is a target for complaints. Refine your email preference center to get a better idea of the content your subscribers want and use that information to create highly targeted emails.
- Make sure the unsubscribe link is prominent, and the process is simple. People will often hit the spam button if they can’t figure out how to unsubscribe.
- Be aware of complaints by enrolling in all available feedback loops. This will ensure that mailbox providers are notifying you of any complaints so that you can remove the subscribers from your list promptly.
Even small variations in your complaint rate can have a major impact on your inbox placement. Keep complaint rates below 0.1% for optimal inbox placement.