Failed to send your message. Please try later or contact the administrator

Contact form 7 is throwing error message whenever trying to send the mail
error is :Failed to send your message. Please try later or contact the administrator by another method.
i have tried :
1. deactivating all the plugins installed
2.Changing the theme
3.Changing senders and receiver email-Id in Contact form edit panel
4.adding WP SMTP plugin and set the port to 587

Am i missing anything ? among the above , i dont now much about setting SMTP options- i followed WordPress plugin support form to set the options , rest are done properly.

Thanks in advance