Sending Welcome E-mails to Newsletter Subscribers

[andauser]

Hello Shopify Gurus,

I am building my website and have configured the double opt-in newsletter subscription for my store. After the user registers to the newsletter, I would like to send a separate welcome e-mail that includes a coupon code. 

With the built-in tool of Shopify, this seems infeasible. I really do not wish to pay for 3rd party apps for this basic - must have - feature. 

Could you help me with that?

Kind regards,

Ayse