Thank you for reaching out to us! That is a great question. So manually adding contacts to your account will not trigger the Welcome email. They have to be signed up via a sign-up form in order for the welcome email to trigger properly. There two things I would recommend for solutions. First, delete the contacts from your account that you desire to get the email and manually add them through a sign-up form. The second option is to create an autoresponder series that triggers when you manually add contacts to your account. Please let me know if you have any other questions!
One of our upcoming webinars in our "Email Marketing Mastery Series", is covering Email Automation!I think you will find this webinar, along with the others we offer helpful!
Here's the link to register for free!