It's not clear what the IRS letter is about. Are they questioning him claiming the child or claiming you. Technically, a spouse can't claim a spouse as a dependent. But, he can file a joint return with his spouse, which is effectively the same thing as claiming her as a dependent plus the other tax benefits of a joint return. It doesn't matter who supported you or where you lived. A husband is allowed to file a joint return with his wife, if she agrees. Period.
If H& R Block prepared his return, he can take the letter to them and they will help with the response to the IRS.
