Simplenews, a newsletter module allows you to send customized confirmation emails on subscribe and unsubscribe actions. The default singe email confirmation for subscribe looks as below,

Subject:

Confirmation for [simplenews-category:name] from [site:name]

Body:

We have received a request to subscribe [simplenews-subscriber:mail] to the [simplenews-category:name] newsletter. To confirm please use the link below.

[simplenews-subscriber:subscribe-url]