Hi,
I was using the Sendgrid plugin to send all emails, and now I installed the Newsletter plugin and it seems that there is a conflict between them.
When I deactivate Sendgrid the "diagnostic test" works fine, but when it is activated the tests give me the following error:
Undefined index: sender_email in /home/citechpasteur/public_html/wp-content/plugins/newsletter/main/diagnostic.php on line 93
PHP Fatal error: Cannot redeclare class SMTP in /home/citechpasteur/public_html/wp-includes/class-smtp.php on line 35
Can you help me? Thanks.