You notice the Channel field blank when creating an E-mail in a Ticket.
Reproducing the Issue
1) Go to Service work center
2) Go to Ticket view
3) Open a Ticket
4) In the E-mail pane create a new E-mail
5) Notice the Channel field blank
The E-mail Channel is meant to be used for processing Inbound E-mails only. That is why in a manually created E-mail this is left blank.
This is the system standard behavior.
KBA , LOD-CRM-EMP , Employee , How To