rarcher30 on "[Plugin: MailPoet Newsletters] Forbidden error when choosing email sender"

I am trying to choose a Third Party SMTP provider through MailPoet > Settings > Send with...

I get the following error when I try to choose a third party SMTP provider (i.e. Gmail):

Forbidden

You do not have permission to access this document.
Web Server at ausidentities.com.au

I have deactivated all the plugins to make sure the conflict is not there. It appears as though it is a server restriction. Could anyone confirm if this is the case or whether there is something wrong with the plugin.

https://wordpress.org/plugins/wysija-newsletters/