Webmail error 550

[retro_viper67]

I've been to trying to send an email through horde.I receive the following error :
There was an error sending your message: Failed to add recipient: xxxxxxxxxx@gmail.com [SMTP: Invalid response code received from server (code: 550, response: Verification failed for <doomsday@doomsday.x10.mx> No Such User Here Sender verify failed)]
Any suggestions?

 

[retro_viper67]

Never mind ,I resolved this issue but i would still complain that the emails sent are received as spam