You can message candidates from within your Welcome to the Jungle account:
Log in to your Welcome to the Jungle company account here
Select "Jobs" on the left of your screen, and click into the relevant job
Select "Messages" at the top of your screen
You will see candidates on the left of your screen; you can select a candidate and message them
If you are posting manually on Welcome to the Jungle, you can bulk message candidates from your "Pipeline":
Log in to your Welcome to the Jungle company account here
Select "Jobs" on the left of your screen, and click into the relevant job
Select "Pipeline" at the top of your screen
Move the candidates you want to message into a relevant stage and click on the box in the top right, followed by "Message candidates"


