You may be here because you are starting your email automation and you have seen this screen below after you clicked Create New Automation.

You may be asking yourself now, what is the difference between "On Subscribe" and "List Name"
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I'm going to break that down for you right now.
​'On Subscribe' is going to be useful when you are bringing in leads either through an Emercury Web form or through a live API feed from a form on your website. So when a lead comes into your list the first message can be sent based on that added time. 

'On List Name' can be used if you already have an existing list with subscribers in it and you want to start an email automation from today with all these subscribers. This means the first email will go out as a broadcast message but your secondary emails can be dripped based on what your triggers are in the rest of your workflow. If the trigger is based on opens or clicks then it will be drip the rest of the way. If the condition is only based on days then this will be sent based in full each day. 

So the big difference is based on sending to subscribers based on when they are added into Emercury which is 'On Subscribe' or if you are starting with a pre-existing list or segment and you want to broadcast a message one time and automate based on triggers or actions after that broadcast message is sent out which is 'On List Name'.

Let us know if you have any questions on which trigger to choose when starting your automation.