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.