Azure DevOps Release Pipeline - Run a task when a specific previous task failed

As a workaround:

1. Add a new variable myspecificstepfails with default value YES

2. Add after your specific step bash or PowerShell task: SetVariable: Initialize or modify the value of a variable

   - bash: |
       echo "##vso[task.setvariable variable=myspecificstepfails;]NO"
   

3. Add the custom condition to your send email

   condition: eq(variables['myspecificstepfails'], 'YES'))
   

In the "Custom conditions" field, enter the condition that checks if the previous task failed:
For example, you can use the expression eq(variables['Agent.JobStatus'], 'Failed') to check if the previous task failed.

Then save your changes.

Related question?

You could get the status through powershell from the api and send email when it's failed. Ensure to get a unique title for the task you want to monitor.

$url = "$(System.TeamFoundationCollectionUri)$(System.TeamProject)/_apis/build/builds/$(Build.BuildId)/timeline?api-version=5.1"

$result = Invoke-RestMethod -Uri $url -Headers @{authorization = "Bearer $(system.accesstoken)"} -ContentType "application/json" -Method get

$taskResult = $result.records | where {$_.name -eq "UnitTest"} | select result

echo $taskResult 

Source for answer: https://stackoverflow.com/a/60611680/12927762

The powershell to roll back task has a way to download the job status and you can use it to look at the status of all individual tasks in a job. I'm not 100% sure this works with the most recent iterations of the Azure Pipelines, but it sure is a way to start:

https://marketplace.visualstudio.com/items?itemName=ms-devlabs.utilitytasks

try
{
   $jsonobject = ConvertFrom-Json $env:Release_Tasks
}
catch
{
   Write-Verbose -Verbose "Error converting from json"
   Write-Verbose -Verbose $Error
}


foreach ($task in $jsonobject | Get-Member -MemberType NoteProperty) {
   $taskproperty = $jsonobject.$($task.Name) | ConvertFrom-Json
   Write-Verbose -Verbose "Task $($taskproperty.Name) with rank $($task.Name) has status $($taskproperty.Status)"
}