Currently, there are two options when it comes to logging emails through the addins:
When sending an email, the Send and log button will log the email sent to all contacts in the To, CC, and BCC fields.
If an email has been received from another contact, the Log button will log this solely against the contact record that sent the email.
This means that an email received cannot be logged against all contacts within the mailing, for example if a contact were to use Reply All to a previous mailing.
If the communication needs to also be attached to other contacts included, this would instead need to be manually added under the communications tab against their contact record in the system.