Referring to the Knowledge Article Chatter post does not trigger Chatter email notifications
, it is the expected behavior not to trigger emails during data migration.
This feature is available for data migration purposes so that when you migrate posts from an external or legacy system, the chatter users are not sent emails for the migrated posts. This can be accomplished by setting the InsertedById to a different value than the CreatedById.
In your case, I assume the InsertedById
and CreatedById
are different and thus no emails are triggered. The article further mentions, if you still want to trigger emails, you can do so by making sure that both the ids are same.
If you want the Chatter post to send notifications to users that have their account configured to receive notifications, make sure while inserting Chatter posts or FeedItems the CreatedById == InsertedById (that is these fields must not be different).
CreatedById
andInsertedById
same when you are trying to load the records?