edit/personalize newsletter block

[itacashop]

Good morning.

My apologize if I'm wrong section for the topic and my english. I used google traslation.
I have a problem for editing the newsletter block.

I'll explain better.
For sending newsletters I use SendBlaster with SMTP server dedicated. To perform automatic management of lists this software takes the emails of a "x" address with the subject subscribe or unsubscribe and updates its database.
To connect it to my E-commerce,  I need to send an email to my address with: sender's = email client, subject = subscribe. the body can also be empty.
I tried to add a function on the blocknewsletter folder in blocknewsletter.php file, the mail() function with all the parameters of the case.
When I go to update the file and upload, the site doesn't work.

Can you help please? Even with a simple link where you can study my problem.
Thank you.