stlg

I’ve got the same problem:

Newsletter TEXT test email NOT sent: try to change the sender data, remove the return path and the reply to settings.

Array
(
    [type] => 8
    [message] => Undefined index: sender_email
    [file] => /var/www/.../web/wp-content/plugins/newsletter/main/diagnostic.php
    [line] => 93
)

Newsletter HTML test email NOT sent: try to change the sender data, remove the return path and the reply to settings.
Newsletter both TEXT and HTML test email NOT sent: try to change the sender data, remove the return path and the reply to settings.

But only while I try to Send few emails with Newsletter and only when I put more than one e-mail address.
I can Send few emails with Newsletter only to one address.

Tomorrow is Monday, and I will reach my webhost.

+seoforbreakfast if you use Google Analytics by Yoast then:
Takayuki advice.

More about this “bug”/lack of information in Yoast plugin:
[resolved] Note change of global function ga() -> __gaTracker()

Different Google tracking codes:
WordPress Contact Form 7 – Tracking Form Submissions in Universal Analytics – by Kathir Vel

Yoast should make tracking function name change explicit and easy to find! It took me few hours, to find a solution :/