I am failing to send mails using my eNewsletter plugin.

I am failing to send mails using my eNewsletter plugin. I am using a third party mail service which gave me the SMTP settings. After putting them, it continues to reject the "from email". I am not sure what to put there, please advise.

NB sorry I failed to select the correct plugin upon posting this message. The plugin is enewsletter not mailchimp integration.