Need more detailed information about email bounces

Not applicable

Re: Need more detailed information about email bounces

I've spent a lot of time working through email deliverability issues with different ESPs and platforms over the years. I do have some issues with the current way Marketo handles some of their hard bounces. To me a Hard Bounce is ONLY true if user is unknown or permanently blocking email from ALL recipients.

To answer your question about categorizing a 4 as soft vs 5 being hard, I've found they are all slightly different based on ISP.

For example,

AOL renders the following bounce codes:

source: AOL Postmaster - Error Codes

  • 554 - Typically Spam, I would categorize as a Soft Bounce, but Marketo will render these hard bounces. Spam complaints generally are time constrained and can be removed after X hours.
  • 421 - Usually related to issues with rDNS records, SPF records, or other issues with the IP and domain relationship. HOWEVER, there are some 421 errors related to spam that appear, which makes this bounce code a bit confusing. Marketo most likely would render these bounce codes as SOFT. (Correct me if I am wrong here). 421 DYN: T1 is one I've had problems with in the past that is related to influx of spam complaints on a new IP.
  • 521 & 550 - Dead email or user blocking email. These are what I would consider true HARD bounces and should never be mailed again. 

Again each ISP is different in the way they render bounces.

The problem I have with the current setup is that its not fail proof. If Marketo wants to categorize SPAM related issues (on the ISP) as a HARD bounce then the following should not show up as a SOFT Bounce.

550 5.7.1 <xxxxxxx>... Denied by Grande Block List - see

I have to dig through my activity log and monitor these bounces quite frequently since we are in the process of warming up a new IP.

What is the solution?

To me each error code needs to be manually reviewed on a frequent based to make sure they get labeled properly. If Marketo wants to consider spam issues a HARD bounce, the Big 5 (AOL, Hotmail, MSN, Yahoo, Gmail) + The Cable ISPs (Verizon, ATT, Grande, Comcast, & Many More!) need to be monitored to make sure the code gets labeled correctly.

Hope this Helps!

Level 9 - Champion Alumni

Re: Need more detailed information about email bounces

Below are  the help articles mentioned in this thread with updated links in the new Community and Product Docs areas.

How Marketo Tracks Email Activity

Email Bounce Codes

Soft and Hard Bounces in Email

Also, there is a new blog post by Ed Masson​,Making sense of Marketo email bounce categories, which expands on Ed's comment in this discussion.

Jep Castelein, is the  Analyzing Email Deliverability ​ document you provided in this discussion current?

Also, I discovered that Marketo does not send emails to leads whose email addresses have an invalid format or characters instead it logs an Email Bounced Soft activity record whose Detail field is 'System send failure: To address parse error...' or 'System send failure: Email injection error'.  These really should haveth eir Email Invalid field value set to 'true',so that they are not included in the email statistics.  Please vote for the   Idea if you agree.

Level 10

Re: Need more detailed information about email bounces

Elliott Lowe​ the document has not updated in the last 2 years, so some things may not be up to date. The main concepts should still apply, but there could be some changes with Smart List details because Marketo changed to a new email engine (from Strongmail to Message Systems) since I wrote the document.

Not applicable

Re: Need more detailed information about email bounces

If there is a doc that you think we should update, let me know : )
Just make sure to @mention me so I see your note..


Level 5

Re: Need more detailed information about email bounces

Is there documentation on what bounce codes trigger Marketo to flag the email address as invalid? Does Marketo ever un-flag the email invalid status?

Level 9 - Champion Alumni

Re: Need more detailed information about email bounces

Ed Masson noted in his reply above that a Category 2 Hard Bounce results in the Email Invalid field value being set to 'true'.  He also has that in his recent Making sense of Marketo email bounce categories blog post.  Also, in the replies to the Monitoring Email Deliverability: Bounces - Part I Marketo Whisper Implementation tips, the Marketo author acknowledged that this was the case. I've submitted a suggestion in the Product Doc that they should add this along with the detailed info about email bounce categories.  Please also submit a suggestion for this in the Product Doc and hopefully Marketo will formally document this.