Fetching E-Mails from crm, there are multiple attributes. If you like to know, who has sent the mail, you need the attribute sender. This attributes contains the e-mail-address.
But CRM also connects the sender with an account or contact, if the e-mail-address field is filled in with the mail address. In my post Connecting e-mails with any entity in CRM you can read the requirements, to have a field and entity automatically connected.
Fetching an e-mail with the connected entity, you have to add the emailsender-field to your ColumnSet. If there is a connection, this attribute will be in your response, otherwise the field won’t be returned.
The attribute itself is an EntityReference and contains the ID and the LogicalEntityName.