In the United States, most churches file for 501(c)3 tax exemption. Some churches choose not to, sometimes as a matter of belief that they should not be "licensed" in any way by a government.
It is my understanding that contributions to such a church are still exempt from income tax, but I would expect closer examination by the IRS of returns claiming such exemptions.
Would such a church, with no official government status, be authorized to accept tax-exempt charitable deductions? How about other tax preferences common to churches, such as real estate and sales tax exemptions?
It is my understanding that in most countries, a church would be required to file for the exemption or would not have it. I have heard the claim that there is an automatic exemption for a church in the US, but it seems to be a controversial claim. I suspect there may be unsettled legal issues related to this, so I ask for a statement of likely interpretation.