In case of default constructors I find that priniting the object can help understand which properties are available (including default values).
This also makes it easier to assign values, for example:

PS > $message = New-Object System.Net.Mail.MailMessage
PS > $message

From :
Sender :
ReplyTo :
To : {}
Bcc : {}
CC : {}
Priority : Normal
DeliveryNotificationOptions : None
Subject :
SubjectEncoding :
Headers : {}
Body :
BodyEncoding :
IsBodyHtml : False
Attachments : {}
AlternateViews : {}

PS > $message.from = “me@domain.com”
PS > $message

From : me@domain.com
Sender :
…