Hi Knox-
If you want to do this (which I wouldn't recommend necessarily), you will want to go to Salesforce options in the Admin section, choose Enable Activities, and select Sent Email or Open Email (depending on what you want). However, these activities will be noted as being "done" by the user identity that you use to sync between the systems. For your reps to be assigned a task for follow-up, you would have to set a FLOW step in your email sends to issue a task activity for the record owner for the activity to be noted by the right individual.
Hope this helps.
Brigid