When you connect mail, you can set up automatic creation of contacts.
This works so if you reply to an incoming email from an unfamiliar email address, then "Contact" will be created. In this case, the customer's email and all email addresses, which are specified in the "Copy" field, will be added to the "Contact" card.
If the "Automatically create contacts for all email addresses with which correspondence was made" check box is checked (only available when the mailbox is connected).
For all recipients, outgoing emails can create contacts. They are created only if there is no contact with such email, or it was not found. Contacts are not created for email matching the boxes, users (free of charge are not counted), robots and system addresses such as noreply@.