Hello Mate, I can help you in " Create simple mailing feature in active admin" As I have reviewed the complete post and assure to help you to help in this. I am willing to discuss more with you.
Relevant Skills and Experience
RoR, MySQL, PostgreSQL, SQLite, HTML, CSS, Photoshop, Bootstrap, Sass, Less, Slim,React, GIT and SVN.\
Proposed Milestones
$222 USD - ROR web development
I am willing to discuss more with you, please let me know what is your best availability.