Automate activation e-mails


I am trying to find a way to automate the e-mails my company send to the requesters so they can activate their accounts (the e-mails notifications don’t suply my demand, i need to be able to customize my e-mail address according to specific companies). My ideia is to create a custom app that send e-mails with some specific triggers, but i don’t know if sending e-mails through a serverless app (or just a web app) will give me the access to get the placeholders that i have at the e-mails notifications.

If i send an e-mail through my own custom app, will the placeholder “{{activation_url}}” work? If it doesn’t, how could i get this value OUT of e-mail notification?

(I didn’t start developing the app yet, i’m first trying to see if it will solve my problem…)
Thanks in advance!