We recently migrated to AEM 6.4 and noticed all OOB workflow Email notification body content which also has URL mentioned pointing to local-host URL on all environments (dev,stage, prod)
This was working on prior AEM version we were on (6.1) and We do have OSGI Link Externalizer Config properly setup for all run modes on 6.4
Apart from externalizer, We do have Day CQ Workflow Email Notification Service (com.day.cq.workflow.impl.email.EMailNotificationService) configured with correct values for Dev/stage/prod but its also not helping.
Can anyone tell if its a product bug or required additional configuration ?
Yes we are using same approach using externalizer.domains to different mode , you can see that screenshot in thread main question.
I dont have any issue using it with our custom notification where I am following exactly same as you mention and it work without any issue.
The issue is only with OOB Workflow Email Notifications which are non customized and I have no idea why they are not having correct URL without populated deprecated externalizer.host property value which if populated like i said above is casing extra http or https issue.