Further developer of Subscribe by Email

Hi

My client want to spice-up the design of the emails send out by the Subscribe by Email plugin.

So I want to hear if you have made use of any filters or hooks in the plugin which I can use to accomplish this, so I would not have to "hack" in the core code of the plugin.

If not, what way would you suggest that I go about doing this, so we can make use of the future updates of the plugin?

Sincerely,
Mika