The Date: header specified in RFC 2822 has been added to the seed data for the example Action Trigger email and SMS templates, but no attempt has been made to automatically modify existing templates. To add this header (and end any "Why are my library emails from 1969/70?" questions you may have heard) make sure the following lines are in all templates that use the SendEmail or SendSMS reactors:

The first is already in most sample templates, but you may need to add it to the top of any custom templates: [%- USE date -%]

And this line should be inserted into the header block of each template: Date: [%- date.format(date.now, '%a, %d %b %Y %T -0000', gmt => 1) %]