Need more detailed information about email bounces

[Anonymous]

The following help articles provide some insight into email bounces, but I can't find any detailed info about the questions below and hope someone can answer these.

• Soft and Hard Bounces in Email
• Email Invalid Cause Codes
• How Marketo Tracks Email Activity

1. Are all the SMTP error codes that start with "4" categorized as a soft bounce?
2. Which of the SMTP error codes that start with "5" are categorized as a hard bounce vs. a soft bounce?
3. Does the Sales Email Bounced event include both hard and soft bounces?
4. Not all hard bounces result in the Email Invalid field being set to "True" - which SMTP error codes cause this to occur?
5. Sometimes there is an Email Bounced Soft event (see details below) that occurs in the Activity Log at the same time as the Email Delivered event or several hours later ?  Is this because the delivery confirmation SMTP message is sent at a point prior to the point at which the bounce SMTP message is sent and if so, does this mean that the recipient likely did not receive the email? Below are the details for the Bounce events.

• NO MATCH DETECTED
• smtp;400 4.4.7 Message delayed
• smtp; 5.3.0 - Other mail system problem 554-'5.1.0 Sender denied' (delivery attempts: 0)    
• 550 [internal] [oob] The response text could not be identified.

[Anonymous]

Hi Elliott,

This KB article has a partial interpretation of SMTP codes:
https://community.marketo.com/MarketoArticle?id=kA050000000KytY

[Jep_Castelein2]

Elliott, I think the link should be fixed now. I put it on my public Dropbox folder. 

[Anonymous]

Thanks Tony, can you provide the mapping of SMTP codes that correspond to Category 1 and Category 2.

Jep, the link you provided goes to Box and requires a login.

[Jep_Castelein2]

Also see some background info in this document: Analyzing Email Deliverability (link fixed again)

[Anonymous]

Hello Elliott!

1.  Yes.  Category 1 (Email Suspended) and Category 2 (Email Invalid) are counted in the mail statistics as hard bounces, all other category numbers are soft bounces.

2.  Category 5 are also categorized as soft bounces.

3.  Sales Email bounces are categorized and handled just like regular Marketo mail bounces.

4.  Yes, category 2 sets "Email Invalid - true".

5.  The first is termed a "composite bounce", that is when a mail is accepted and then rejected during the same SMTP session.  In this case, that does mean that the mail recipient most likely did not get the mail delivered to their inbox.  If a mail is bounced much later, that means that it was accepted during the initial SMTP session, but then was rejected when the recipient server, for whatever reason, is unable to complete delivery to the inbox for the intended recipient.  This usually is an email that MTA sends back to us, which allows us to record the bounce.