Hi Mary
Yes, they are linked to Interaction log entries which you can access form Contact, Salesperson, Sales Quote... However there are few preconditions that need to be in place for this to work.
You need to have customers and vendors set as contacts and they need to have their email addresses in their contact details.
You need to have salesperson email addresses as well set in sales person record.
You need to enable email logging feature (video).
You need to enable Business Inbox feature as well.
Once all of above is set, email logging will link emails exchanged between salesperson/purchaser and customers and vendors.
Scenario: Lets say customer Microsoft asks Peter for quote and he's out sick so his colleague Annette answers.
What you see in interaction log entries for contact is:

Line 1: Email came in from Microsoft (for demo purpose) to salesperson 1 (Peter)
Line 2: Peter forwarded his email to salesperson 2 (Annette)
Line 3 and 4 - Annette prepares sales quote
Line 5: Annette sent quote to customer
You can see that lines with interaction template EMAIL have attachment set to Yes. Clicking any of these opens a linked email (both Annetee and Peter can access emails linked to interaction log entry).
This is the full email thread for which Interaction log entries were created
