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Recently my team was managing a customer escalation about an unexpected and suspicious spike in click activity in email.  The customer observed all the links within an email activated immediately after delivery.  This is a known issue with filters like Barracuda. The email is accepted and if the message is deemed suspicious, it is subjected to higher scrutiny and the links are validation ‘tested’ to ensure they are not malicious. We have seen a slight increase in this activity since the beginning of the year but in most cases we can mitigate the behavior by focusing on improving the reputation of the sender.


At issue is a part of the Barracuda email filter call the intent filter. There are 3 different modules to this filter.

Intent analysis – Markers of intent, such as URLs, are extracted and compared against a database maintained by Barracuda Central.

Real-Time Intent Analysis – For new domain names that may come into use, Real-Time Intent Analysis involves performing DNS lookups against known URL blocklists.

Multilevel intent analysis – Use of free websites to redirect to known spammer websites is a growing practice used by spammers to hide or obfuscate their identity from mail scanning techniques such as Intent Analysis. Multilevel Intent Analysis involves inspecting the results of Web queries to URLs of well-known free websites for redirections to known spammer sites.  According to Barracuda support it is the multilevel intent analysis module responsible for clicks on links.


Often in these cases the bounces returned from other undelivered email show evidence of content filtering by other networks also, which may indicate there's something going on with the content that's making it look suspicious. In addition we always coach customers to avoid the usage of any URL shorteners also. If there are any in your content, that may prove problematic.


How to Manage This Behavior?

One of the ways we suggest mitigating this behavior if it is problematic is to consider set up a “stealth” link, that human readers won’t see or click on but that parsing software might. Clicks on that link, that is unseen by human eyes, are a sign that the click was not done by the intended recipient. It would allow you to create program rules around the behavior so as to mitigate skew in the click rates.


I also suggest reviewing your own email sending reputation to understand if your own reputation is triggering this activity.  Are you managing your in-active addresses and removing those from your email program over time?  Do you have a process to remove recurring Soft Bounces after successive unsuccessful delivery attempts?  These two processes are often the first place my team starts when working with customers to improve their sending reputation.  Taking these two actions will improve your reputation over time and you will be less likely to trigger enhanced content filtering if you maintain a pristine sending reputation. 


Here is a great series of Community Resources to help you understand and manage your email sending reputation:


Also, here's a link to an article by a well known deliverability expert on this topic from a couple of years ago but is still relevant:

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The Email Deliverability and Privacy Team always stresses the importance of a strong sending reputation. By keeping an eye on your engagement (opens, clicks, etc.) and reputation (spam complaints, spam traps, unknown users, etc.) metrics you’ll get a good picture of how your emails are being received by subscribers.

But if you’re looking for another measure of your reputation you can take advantage of a handful of resources that will let you know where you stand.  Here are 4 sites that will help you check sending reputation:

Like a credit score, a Sender Score is a measure of your reputation. Scores are calculated from 0 to 100. The higher your score, the better your reputation and the higher your email deliverability rate. Numbers are calculated on a rolling 30-day average and illustrate where your IP address ranks against other IP addresses. This service is provided by Return Path.

Senderbase is a product of Cisco and provides you with the tools to check your reputation by ranking you as Good, Neutral, or Poor. Good means there is little or no threat activity. Neutral means your IP address or domain is within acceptable parameters, but may still be filtered or blocked. Poor means there is a problematic level of threat activity and you are likely to be filtered or blocked.



WatchGuard’s ReputationAuthority helps protect business and government organizations from unwanted email and web traffic that contain spam, malware, spyware, malicious code, and phishing attacks. You can look up your IP address or domain, receive a reputation score from 0-100, and get the percentage of emails that were good versus bad.



TrustedSource is a site very similar to, but run by McAfee. It provides information on both your domain’s email and web reputations as well as affiliations, domain name system (DNS), and mail server information. It also provides details on the history, activation, and associations of your domain

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Set Up Google's Postmaster Tools

If you send a large volume of emails to Gmail users, you can use Postmaster Tools to see:

  • If users are marking your emails as spam
  • Whether you’re following Gmail's best practices
  • Why your emails might not be delivered
  • If your emails are being sent securely


Customers are able to leverage Google's postmaster tools by setting up a TXT record for their From Address domain.

Does not require a dedicated IP and does not require Marketo to set up DNS for the customer.

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If you are experiencing email delivery issues to AOL, chances are you need to improve your sending reputation. The best way to ensure you have a good reputation is to send timely and relevant email to an active and engaged audience. The following are some suggested best practices for sending mail to AOL. While each of these best practices should help improve your sender reputation, they do not guarantee whitelisting or email delivery.


  • Ensure that you are only sending mail to users who specifically requested it. It is not advisable to purchase mailing lists or subscribe users by having an opt-in checkbox automatically checked on your website.
  • It is preferable to have a double/confirmed opt-in process. When users subscribe to your mailing list, send them an email asking them to click to confirm their opt-in. This will reduce the number of people who sign up from fake email addresses.
  • When users subscribe for your mailing list, tell them what mail to expect, how often to expect it, and what it will look like. Set recipient expectations clearly.

Authenticate with Domain Keys Identified Mail (DKIM). This will provide you with a consistent reputation across your domain, regardless of what IPs you send mail from.  Work with Marketo Support to set this Authentication up.

Address Book

Send your email from a consistent email address and advise your users to add that address to their address books. Mail sent to users with your address in their address book will be delivered to the inbox with images and links enabled.

Database Management

AOL is sensitive to engagement by your recipients.  Are you reviewing and removing address in your database that have not engaged with your email in 6 months to year? If not you may want to leverage the following Smart List example to review and then remove your inactive recipients.


Identifying Chronic Non-Responders/Unengaged

Identify chronic non-responders or those unengaged with your email marketing to:

  • Target for a re-engagement program
  • Changes status to Marketing Suspended to remove them from active campaigns



Easy Unsubscribe
  • Provide an obvious and visible unsubscribe process in your mail.  Add this to the top of your email as well as in the footer.
  • Make it easy for users to unsubscribe from your mailing list.
  • Ensure the unsubscribe process is easy to use, such as a one-click unsubscribe web page.
  • Users should not have to log into a website in order to unsubscribe.
  • Process unsubscribes immediately.
Invalid Recipients

A high number of invalid recipients will harm your reputation. You can reduce the number of invalid recipients on your list by using double/confirmed opt-in. You will always have some invalids due to people changing email addresses, but the lower the number, the better your reputation. Marketo removes invalid recipients from your list immediately after the first bounce.


Brand your mail so that recipients can quickly identify it and won't mistake it as spam. Make sure the from address of your mail clearly identifies who it is from. Also, include your brand in the subject line. Even if users want your mail, they may not recognize it right away. Subject lines like "Your daily newsletter from 'Company'" or "Your monthly 'product' update" help the user identify mail they want. Even if you have a confirmed opt-in list, users may not recognize mail as being from you with a subject line like "Buy two, get the 3rd one FREE!!!" and may report it as spam.

For more sender best practices, read the Messaging Anti-Abuse Working Group's Senders Best Communications Practices Version 3.0 (Adobe Acrobat/PDF).

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