I got this kind of error saying “Failed to send your message. Please try later or contact administrator by other way.” after installing the plugin Contact Form 7. And so I suspected that my server is not properly set for mail sending. But I noticed that I was able to received emails from the comments of my visitors generated by my server. So that makes me think that there is something wrong with my plugin Contact Form 7 and not with my server. I checked my Contact Form 7 settings if it was properly configured or not. And I tried changing the values of the field until i found it.
As you can see, I only replaced my value for the FROM with the firstname.lastname@example.org which yourdomain.com is your domain where your wordpress website is installed.
Hope that helps.