The people you send a transmittal to are called recipients. The recipients can be any combination of internal and/or external participants.
If you assigned a distribution rule to this transmittal on the General tab, the recipients list is automatically populated with the participants that are assigned to the selected distribution rule. You can add more recipients, but you cannot remove recipients that are automatically added through the distribution rule. If you did not select a distribution rule, then you must manually add all of your recipients.
The Add recipients dialog opens.
The Participants list (upper list, not labeled) displays the current project participants. You can filter the list to show only internal participants, only external participants, or both internal and external participants.

You can use this dialog to add any current internal or external participant to the recipients list.
You can also use this dialog to invite new external participants to the project. Once invited, you can immediately add the newly invited person(s) to the recipients list (you do not have to wait for them to accept the invitation in order to issue the transmittal).
The participants are added to the Selected users list (lower list).
The Invite external participant dialog opens.

A default subject is provided, which you can keep or change as needed.
An invitation is sent to the person, and they are added to the external participants list.
The newly invited external participant is added to the Selected users list (lower list).
The selected participants are added to the Recipients tab of the Transmittal Draft dialog.

The purpose selected on the General tab determines the default settings for the Ack and Resp options for manually added recipients and whether or not they can be changed. When the transmittal requires a response (as determined by the selected purpose), the Resp option is turned on by default for all manually added recipients. You can turn this off as needed for some recipients, but at least one recipient in the list must have the Resp option turned on in order to issue the transmittal. When the Resp option is off for a recipient, they cannot respond. When the transmittal does not require a response, the Resp option is disabled for all manually added recipients, and cannot be enabled.
Other team members will still see a record of it (name and ID) in their list of incoming submittals, but they will not be able to open it. The administrator and the transmittal author and issuer will always have access to it.