I was working on a project where i used "SMTP Authentication Support" module to send emails. The authentications i provided were my personal gmail account details, It was working fine. Now when i am entering the site admins account details its displaying "Unable to send e-mail. Contact the site administrator if the problem persists." error. It also says that "SMTP Error: Could not authenticate." Can anyone let me where i am going wrong.
I would suggest you to use the module Mandrill
First you can go to mandrillapp.com and create an account.
After account creation go to Api and generate an Api key.
Then after installing the module on drupal instance. Go to Configuration->Mandrill->Add the Api key and your site is ready to send mails.
Hope this helps.