Will the welcome email send to existing list contacts?
The welcome email series automation is based on the date that your contacts subscribed. The first message in the series will only send to subscribers added after you start creating the automation. This means that if we create and start the welcome series automation right now then existing contacts won’t be sent the first email in the workflow.
What to be careful of when creating the welcome automation in Mailchimp
Because the workflow calculates who to send to based on when you create the welcome series there can be issues if you keep the workflow in draft. If, for example, you create the workflow today and only activate it in a month then all people added to your list from today will be sent the first email in the automation.
The best, and safest, means of avoiding issues is to create and active your welcome series automation in quick succession.