Making sense of Marketo email bounce categories

Level 10
Level 10

There is many websites out there that can help walk you through email bounced codes, categories and examples. What I wanted to cover here is how Marketo handles bounce categories and what they are. For some time now, I had a hard time trying to find information regarding Marketo’s bounce categories and then try to report on them.

Working with Marketo support over the years I was able to nail down some of them.

Was told that there are 6 categories but not in numerical order. I’m not too sure what categories 5 and 6 are. I’ve not seen any leads being tagged with them, but I’m sure some of you may know them and can add to this post and we can all reference them.

The point of this is to monitor and find repeat offenders in case of deliverability issues. With adding a constraint of say last 7 days depending on your email frequency should help you get an idea of the data that needs suspending.


The Marketo mail servers use "StrongView” (formally StrongMail) as there mailing software. (At least they did when I went though this few years ago with Marketo support). StrongView stamps emails with 1of 6 different bounce categories. StrongView categories are blocking (receiving server is not allowing mail), hard (unknown user), soft (temporary failure) and technical (infrastructure).

To identify these categories, we will set up a smart list for each of the categories, set them to look at the last 7 days and show me the leads. So lets make a start!

Email Management

  • Create a new folder and name it Email Management
  • Create 6 Smart Lists


The categories

Category 1 – Should be Email Suspended (usually from spamblock). You may find leads (particularly Gmail addresses) that are Category 1 bounces, but have no data in Email Suspended or Email Suspended at. They are STILL problematic leads. You could also add a further constraint for the # of times they hit Category 1.



Category 2 – Email Invalid. Anyone who has a Category 2 bounce should be email invalid. Leads in this category should be considered for being marked email invalid if they are not already.

Category 3 – Soft Bounce. “Mailbox is full”, that kind of thing. Temporary. Repeat offenders may be an issue.


Category 4 – Technical. Something was wrong with the mailserver on the other end. Again, temporary, but you might want to look for minimum # of times.


Category 7 – Proprietary, used for Strongmail internally.

Category 8 - Is invalid From Email address

The most common reason this happens is because your "From" email address is incorrect. The easiest way to check this is to go into the results of your campaign, and do a search at the bottom for ‘email bounced’. When results come up, double click on a random one. It will show you the reason for the bounce.


Category 9 – Unknown. Nonsensical errors, non English, etc.

I hope some of this is helpful, this information I gathered was from a few years back but may still be relevant today.

Please feel free to add and more information to this post.

Not applicable

Nice work Ed.I never knew the categories even existed.

Do you just keep track of these categories or do you also have data update programs that do something with them?

Level 10

Thanks Jeff!

I just monitor how many email addresses are getting flagged every 7 days category .

I place the smart list for each category in to a Lead Report as custom columns and have that email me every week for the last 7 days.

Not applicable

Thanks Ed, excellent post.

I tried modeling the smart lists you setup.I had a couple of questions.

Category 1 - Works as described.

Category 2 - Works as described

Category 3 - Could not find any results. These are soft bounces so it makes sense to use "Email Soft Bounce is any" smart list?

Category 4 - Also could not find any results.

Do you use any additional smart lists for category 3 and 4 to spot check?

Level 10

Remove any date constraint to see if that will generate numbers for you in a smart list. If you don't have any, thats good. Don't worry.

The main thing is having them to check every so often incase you may have a deliverability issue. The main insight will be what is populated in the reason columns in activity history.

From here you can add another filter for 'email Invalid cause' and use Contains xxxx to nail down on a recurring reason issue.

Not applicable

Ok thanks. Makes sense for category 3. I removed the constraints and just added Email is any and category is 3 and still received no results. However when I did the same thing for Email Bounce Soft is any I get quite a few results. These two should be the same correct?

Not applicable

Ed - thank you for putting this together. This is of tremendous value, especially for instances that are starting to see deliverability issues. It is definitely not documented properly on this site or any other Marketo resource I could find.

Thank you very much.


Level 5

Thanks Ed, great stuff. Question about category 3 - in your screen shot I see some of those soft bounces were marked as invalid email addresses by Marketo. What do you do with those? Do you mark them valid again?

Level 2

Great post!

Not applicable

Very helpful post. Good work Ed

Level 10

I tend to give repeat soft bounces up to 3 times before making them invalid.