Separate Returns Need Separate Envelopes
The IRS advises exempt organizations and persons who prepare returns for them that an organization’s annual return and its unrelated business income tax return (Form 990-T), if required, should be mailed in separate envelopes. In addition, supporting statements for Form 990-T should not be attached to an organization's annual return. This will help to reduce errors and expedite processing of these returns.
Another way to reduce errors and expedite processing is to file electronically.