Email invitations sent to .co TLD domains are not being delivered.

I have been trying to add my g**@****.co email address to my bitbucket account for a while now to no avail. I have tried to add the email, and resend the invitation multiple times. It is currently sitting in an unapproved status on my account.

I recently sent a coworker a similar invite to b**@****.co, and he has reported that as of the writing of this issue he has not yet received it.

Could this be an issue with .co TLD's? My *****.co email is hosted via Rackspace, but so are the other two email addresses I have (a .net and a .com) and those work perfectly.

Please let me know if I can provide any more detail to help you debug this.