Domestic Mail Manual (DMM) 243.2.1* provides that mailable matter that is neither mailed or required to be mailed as First-Class Mail or Periodicals may be eligible for Standard Mail rates. DMM 233.2.3* prescribes that matter containing personal information must be mailed as First-Class Mail or as Express Mail. Personal information is any information specific to the addressee.
A check which is made payable only to the addressee or only to a specific individual, i.e., “Pay to the order of John Doe,” “Pay to Jane Doe or order,” is considered “personal” information and generally is mailable only at the First-Class rates of postage.
A printed (computer-generated) bearer check, that may be negotiated by anyone who presents it for payment would be acceptable at the Standard Mail rates. Examples include those styled to "Pay to John Doe or Bearer," "Pay to Bearer," "Pay to Addressee or Bearer," “Pay to Cash,” “Pay to the Order of John Doe or Bearer,” “Pay to the Order of Bearer” or “Pay to the Order of Bearer or John Doe Addressee.”
Since the $5.00 rebate check in the example is a “bearer” check that can be negotiated by anyone, it does not have the characteristics of “personal information” and is therefore, not required to be mailed as First-Class Mail. The bearer check may be mailed at the Standard Mail rates.