An email was expected to sent out on a specific cast of Nurture Program but a specific lead or couple of records did not receive it.
There are a number of steps to begin troubleshooting this query and here is a flowchart how to proceed.
1). Check if engagement program is turned on from its setup up. Also check if at the time of email cast, the program status was on (this can be checked from Admin>Audit Trial)
2). Check if the email asset which was expected to send was present in the Nurture Stream at the time of cast. Also check if that email asset was activated (having green arrow). Both of these can be checked from Audit trail where you will find the log of "Add Email" and "Activate Email" along with its date/time.
3). Check if the lead is present in that specific stream using the smart list filter "Member of Engagement Program > Stream = <required stream>"
4). In the same smart list, use filter of "Engagement Program Cadence Changed" and set "New Value = Paused" and see if that lead qualifies it or not. A paused cadence would mean the lead has been temporarily restricted to move in the flow of nurture stream and hence will not received any email content.
5).
Most important step- Go to the activity log of lead and search for the engagement program's name in the quick find bar. Look for all logs along with their dates when the lead performed any activity related to that engagement program like added to program, changed cadence, removed from program, etc.
6). In continuation of step 5, check in the activity log if the lead was added to engagement program in less than 25 hours before the next cast by looking at the time of log "Added to Engagement Program". This is because as per the doc, the lead must be added atleast 25 hours before the cast to abide by the recipient time zones otherwise it will skip that current cast and will qualify for the next cast.
Schedule Engagement Programs with Recipient Time Zone | Adobe Marketo Engage7). In continuation to step 5, check if the lead was moved to a different stream via getting qualified into transition rules. Transition rules are present in stream of those engagement programs that have more than one stream and are used to move leads from one stream to another.
Transition People Between Engagement Streams | Adobe Marketo Engage8). Check if the lead is unsubscribed, email invalid, email suspended (this one is only valid for 24 hours), marketing suspended or block listed because any of these 5 conditions would block the lead from receiving any communication from any of the Marketo's program or campaign.
9). Check if the record has hit the communication limit. Go to Admin>Communication limit and see what we currently have setup. If limit is 2 emails per day, then create smart list "Was sent email>Email Is ANY> Minimum Number of times 2" and see if lead qualifies in it. Alternatively you can go into lead's activity log and manually count number of "Send Email" logs in last 24 hours and in last 7 days and match it with the communication limit of Admin tab.
Using programs as stream content:We can also use programs (default and event) in nurture stream instead of direct email assets.
10). In case of using a program, the email can be sent out to the required audience only if that program have a smart campaign with filter "Member of Engagement Program>Name of Program" and flowstep of "Send Email". So make sure the smart campaign has these configurations. (Make sure the campaign has to be a batch campaign and not trigger)
11). If above pointer is true still record is not present in the result tab of the campaign, then check all steps from step 1- step 9. If nothing is found then check if smart list has more than just "Member of Engagement Program" filter and if the lead is failing to qualify any of the other filter.
12). Check in the schedule tab if qualification rules says "Each Lead can qualify only once". If yes then go to campaign member tab and search if lead is already a member, if yes then lead will not qualify again and this is why email was not sent.
13). Check if flowstep has a wait step and the lead is stuck there because wait step does not create any log in the results tab. People in waitstep can be checked from dashboard of the smart campaign.
14). For any other possible reason why the lead did not qualify the smart campaign, you can look for the knowledge base "Lead not qualifying smart campaign- Universal Checklist" under heading of Batch Campaign:
marketo.my.salesforce.com/articles/en_US/Article/Lead-not-qualiying-smart-campaign-Universal-Checklist?popup=true
15). If all above pointers have been checked still unable to figure out why the email was not sent on a specific cast, escalate the case to Tier 2.