A Subject Template controls the behavior of any Subject Line information used in a message passed through this template. Since Subject Templates may be applied on a Global, Carrier, Connector or Recipient level, it is entirely possible to create a standard format for all Message Subjects using a Global Template, then specify exceptions to this global rule in the Carrier, Connector or Recipient templates.
Generally speaking, the SMTP or Email protocol is the only protocol that actively references the Subject line during its protocol negotiation sequence. As such, you may want to format special Subject Templates for each of your SMTP carriers but that is not required. This can be also accomplished by a single Global Template, if you want to apply these settings to all messages.
Please see the Macros section for a list of variables that can be used in this section.