I am getting the error "Server response: 451 451 Temporary local problem - please try later" when sending password reminder emails via Laravel and Mailgun. I am running Laravel on VirtualBox.

I set up VirtualBox using Vagrant, would this have made a difference?

If I change the SMTP settings to my own host it works absolutely fine. Is there an issue with using Mailgun on a Virtual machine?

Update

I can send to Gmail addresses without any problems, however, they apparently are neither being blocked or allowed.

This is the error I get:

Failed: support@mydomain.com → me@anotherdomain.com Server response: 550 550
Verification failed for bounce+ad0324.1a1312-me=anotherdomain.com@mydomain.com
No Such User Here Sender verify failed