I like to do this job.
I'll create a modern and attractive pop up matching with thmem, it'll be totally adjustable with all standard screen size.
I'll store data to db, and i'll attach function with post, so when ever you publish post email will send to all emails in that db list.
I'll add validation of all type.
pop up will show how you want once, or every time or once a year etc
I'll use advance technologies like, PHP, MySqli, HTML5, CSS3, Jquery, JSON, Ajax, and Bootstrap, as per required
I'll give you 2 weeks free support in regards of this project
so let start discussion and start project, and thank you for reading