Hello there.

Is it possible to use a newsletter extension (like AcyMailing or Mailster ) with this template?

Thanks

Yes of course you can use any extension with our theme
But it is not recommended to use many Joomla extesnions, because you dont know if the extension is working with the next Joomla update.
I would prefer an external solution like mailchimp. You can insert the mail chimp form into any module or content.

That's ok, I just want to use an extension in order to collect visitors' email address.
Newsletters and all that stuff will be handled by a specific software.

Thanks.