Changed MX Records, and now emails are bounced back

Changed MX Records, and now emails are bounced back

I changed my MX records since I changed my hosting service, and now e-mails are bounced back with this message:

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain mydomain.com.ve  by mydomain.com.ve  

The error that the other server returned was:
550-Please turn on SMTP Authentication in your mail client.
550-mail-qa0-f45.google.com [209.85.216.45]:33116 is not permitted to relay
550 through this server without authentication.

Any ideas why this is happening?