In offering a premium email delivery platform to our customers we carefully monitor our IPs for listings on blocklists (Top Blocklists – What You Need to Know.) The Marketo Privacy team maintains relationships with the major blocklists to better assist our customers in resolving these issues. When we find that one of our customers was responsible for a blocklisting we contact that customer and request some actions be taken to remediate the issue.

In many cases we find that sending an email to a spamtrap address (What Is a Spamtrap and Why Do They Matter?) caused the blocklisting.  Spamtraps are email addresses that have either never been used or have not been used for a long time and are now owned by anti-spam organizations. They are considered by these organizations as a sign of poorly maintained or inappropriately acquired addresses. Based on this assessment they conclude that the marketer is sending spam and consequently blocklist the sender. 

To prevent future blocklistings you'll need to review your recent activity to remove the spamtrap from your mailing. Finding the spam trap address can be difficult; they are closely guarded secrets of the blocklisting organizations and they do not share these addresses.

We describe several strategies below. The best approach for you depends on the make-up of your database and the amount of behavioral history in your Marketo system.The goal is to isolate potential spamtrap addresses and remove them. The group of addresses you select should be broad enough to capture those potentially bad addresses but small enough not to suppress a huge portion of your database.

Blocklists are not all the same - some provide Marketo with more information, some with less. If at all possible we will provide you with a date and a subject line to help you isolate potential traps. 

Step 1

        To narrow the list of potential traps you should consider the following:

    • Have you recently added any new leads or new lead sources?
    • What is the source of these leads? Any purchased or appended email addresses should be removed because these data sources are often the source of newlyintroduced spamtraps. In addition lead sources like this can violate Marketo's Email Use and Anti-Spam Policy
    • Have you recently added any older leads from another database that have not received email in the past year?  Some email providers will turn an address into a spamtrap after a year of inactivity.  If you have a list of addresses that had not received email for a year or more before recent email campaigns this list should be removed.
    • Does your system use any custom fields to indicate customer status, event attendance, recent contact with your sales team, or other forms of engagement?  Take advantage of this and isolate the inactive or nonresponsive segments of your database using all activity data you have available.
    • Is there anything different about this specific mailing that makes it different compared to your previous email campaigns?
    • Did you send any other mail on the same day?  You could compare the recipient lists.

Step 2


If you were able to identify newly introduced email addresses to your email program that are likely the source of the spamtrap suppress or remove those from your database so they will not receive email in future email campaigns. 


If you have not identified a specific data source than you should target the inactive or nonresponsive segments of your database for potential spamtraps.  Because an individual does not manage spamtrap addresses, they are generally part or a larger spamtrap network; they will generally not show any form of activity. If you have behavioral history, the best approach to take is to identify the people who are not interacting with your company - not opening or clicking emails, not visiting the web page, not attending events, etc.


Build an inactive Smart List using ALL filters:

  • Was sent email the day of and day before the spam trap hit (please contact for the date of the trap hit if you do not have this information already.)
  • Lead “was created” date is at least 6 months ago

Inactivity Filters

  • Not visited web page is “any”; constraint date of activity “in past 3 months”
  • Not filled out form is “any”, constraint date of activity “in past 6 months”
  • Not clicked link in email is “any”, constraint date of activity “in past 6 months”
  • Not opened email is “any”, constraint date of activity “in past 6 months”

If you have custom database fields that would show other forms of activity feel free to add this into your inactive Smart List to exclude active leads.


Step 3


Once you have created a smart list to identify these suspect leads you have several options.

[Leads Tab > Lead Actions > Flow Actions]

Remove leads from database

Why waste your time on inactive leads?


Set leads to Marketing Suspended = true to suppress from future mailings

Marketing suspended is functionally equivalent to unsubscribe. These leads will still be available for other flow actions, tracking, or operational emails. To avoid suppressing an active lead’s email address you can create a daily recurring batch campaign to take any marketing suspended lead who "wakes up" and engages and set them back to marketing suspended is false. 


The daily batch campaign would be set to change Marketing Suspended back to false if the lead performed any specific activity in the last 24 hours like if they visit a web page, open or click a link in an email, fills out a form or has a lead status change. Here's how to set up the campaign:


Smart List (using the "ANY" filter, not "AND"):

  • "Visits Web Page"
  • "Clicks Link in Email"
  • "Fills Out Form"
  • "Opened Email"

          All selectors for these filters should be set to 'any'.



  • "Change Data Value" flow step
    • Attribute: "Marketing Suspended.
    • New Value: "False".



Opt-In reconfirmation pass

Create and release an email to inactive list with the following sample copy: "We have not heard from you in a while. Click this link to continue to receive messages." Anyone who does not click the link within 2 weeks should be set to Marketing Suspended. For recommendations on successful reconfirmation messages search our help articles on Successful Reconfirmation.


Some mix of the above

Many of our customers take a tiered approach to blocklist remediation. If they can identify inactive, low-priority leads they may choose to immediately delete or Marketing Suspend these while reserving a reconfirmation pass for higher priority leads. If your list includes extremely high value sales targets you might consider having your sales team reach out individually. If considering this approach we recommend that you export the list and try various sorting techniques to get a feel for the leads you're looking at before deciding on the best way to segment them for different tiers of attention.



Step 4

You’re Done! Don't forget to fill out the delisting form




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