Hey @Nolwww !

My responses are in blue below:

1. If the user connects on two different devices (and thus have two device_id aaaa and bbbb), will Amplitude reconcile the two device_id, as long as there is the user_id associated with both device_id? (I assume that’s the case, but I just wanted to make sure)
   As long as the user_id is the same for aaaa and bbbb, Amplitude will recognize them as the same user and merge events into one profile. In the profile under Device IDs, you will see aaaa and bbbb (and any other device_ids that perform events with the same user_id)
    
2. Can I use the e-mail address to reconcile events? For example, if I have 10 events with only the device_id (= aaaa), and one event with email (example@gmail.com) + same device_id (aaaa), can the e-mail be used to reconcile the events having device_id aaaa?
   ALL events performed by a specific device_id will be logged under one Amplitude profile. In the above example, the Amplitude profile for device_id = aaaa will show the 10 events that only had device_id AND the 1 event that had device_id and email
    
3. If I have 10 events with session_id aaaa and e-mail example@gmail.com, and 10 events with session_id bbbb and e-mail example@gmail.com, can I reconcile session_id aaaa and bbbb ?
   Amplitude will not automatically associate users by email address, unless you are setting the email address as the user_id (I am assuming you are not). So if the sessions above are performed by different device_ids with no user_id, the activity will not be merged into a single profile. 

I found this article very helpful for understanding how Amplitude tracks/identifies users: https://help.amplitude.com/hc/en-us/articles/115003135607

Hope this helps!

Hey @Nolwww 

1. Yes, that’s correct. Amplitude will tie the events on two different device_ids to that same user_id after it has associated the device_id+user_id mapping.
2. Assuming the email address is set as a user property and there is no user_id established yet. If yes, then all the events will be tied under device_id aaaa and example@gmail.com will appear as a user property on all events after that event. The user will still be anonymous since there isn’t a user_id yet.
3. If they are coming in as two different device_ids, then they will be appear as separate users irrespective of session_id and email address. So there is no reconciliation happening over here.

I would recommended reading this article on how Amplitude tracks unique users.

Hope this helps.

@SheenaGreen Did you also come across the Insided Spam Filter Ghost on this one?
Strangely I couldn’t see any posted reply to the above before I posted mine.
 

@Saish Redkar it’s always good to get your answer validated by the community expert! 

Thank you @SheenaGreen and @Saish Redkar for all the ways you support others!