My site has already over 10,000 existing users. I have recently decided to have newsletter feature on my site. The Newsletter plugin is super awesome. I can embed a subscribe form on my site. But if an existing user subscribe again with the same email as he/she registered at my site before, will he/she get a problem? Is it possible to ingrate all the existing users to newsletter subscribers? Last thing, can I add “Name” field in the subscribe form(Currently subscribers need to enter their email address)? Cheers.
I do not understand what you means with the first sentence about the subscription with the same email. If someone register to your newsletter with an already registered email nothing of special happens, there will be only one subscriber.
When you “import” the actual WordPress users, an entry for each user is added to the subscription list with the user email.
About the second request, the subscription form can be configured on subscription steps panel.