"Email invalid" yet "email delivered"

[Milena_Volkova]

I have records that have both "bounced" (with the message "550 [internal] [oob] The recipient is invalid", which I thought to be hard-bounced) and "delivered", within minutes. 

I am reading this post: https://nation.marketo.com/t5/knowledgebase/email-bounces-with-error-quot-550-internal-oob-the-recip... it appears that those bounces and the related messages are not very reliable after all. I ran one of the email addresses from my "hard bounced" list through https://www.verifyemailaddress.org/email-validation and it seems to be valid. However, I can't check every single email one by one, and because it's marked as "email invalid" in my instance, I can't communicate with this person by email anyway. Should I still delete this record or mark it "no longer at the company", even though the email might be valid and therefore the person is still at that company?

Can someone please recommend best practices for what needs to be done for hard bounces? Thank you.

[Darshil_Shah1 · Accepted solution]

Well, I'm assuming that when the email was sent, these records did not have their Email Invalid field set to True (else Marketo would not have sent them the email anyway).

Also, a delivered activity in the activity log doesn't necessarily mean that the message has been successfully delivered to the recipient's inbox. Certain categories of soft and hard bounces only register after the message delivery SMTP notification is sent back to the sender. In this case, the activity log will show a delivered activity followed by a bounced activity. As Sandy mentions in his comment here - by the time the recipient's MX server sends the bounced notification to Marketo, it's too late to send an actual SMTP-level rejection and hence can't undo the delivered notification previously sent. 

[SanfordWhiteman · Accepted solution]

Absolutely right, Darshil.

SMTP is a store-and-forward architecture, meaning that a message is processed over several “hops” before it gets to the final destination server (the mailbox server). Along the way, a message can be accepted (meaning accepted to be forwarded) or rejected.

We hope for rejections to happen in as few hops as possible, but that’s not always the case. When Marketo’s outbound server connects to the MX for a domain, that MX may say everything’s good, but then it tries to forward to the next hop and comes up with a hard rejection. It then has to send a new bounce message back to Marketo. By that time, the Activity Log has already been updated with Delivered because the first external hop was indeed delivered.

[Milena_Volkova]

Thank you, Sanford! 

Re: Marketo marking Email Invalid = True when an email bounces - is that an out-of-the-box functionality? Did you find that to be reliable in the sense that only truly invalid addresses are marked that way? 

[Darshil_Shah1]

Yes, this is the OOTB functionality. This prevents Marketo from sending out emails to addresses that are invalid (i.e., the ones that encountered hard bounce due to the address being invalid or are entered in the system as wrongly formatted in the first place). IMO this OOTB functionality is reliable enough as it basically looks for bounce activities in the person's activity log, and as long as Marketo is able to receive email-rejection notification from the recipient's MX server, it should technically set the Email Invalid field to True.

Please add/update in case I've missed anything, Sandy. Thanks! 🙂

[SanfordWhiteman]

I find it reliable. It does have to use pattern matching on bounce message text (since you don’t have the real SMTP error code to look at directly anymore) but for this targeted case it’s not a worry.