We filed our 2019 return earlier this year and forgot to sign it. We received the return with a form 3531, box 1 checked indicated lack of valid signature. We do not have the envelope that we received it in, so not sure what the return address was. Should we send to the same address that we originally sent to, or one of the Submission Processing Centers? If the latter, which one? No payment will be enclosed.
Forget to sign the form 1040 where to send form 3531 back to IRS
The IRS should have provided a return address on the envelope you received your Form 3531 in. If you do not see an address or if you discarded the envelope, please refer to this link to find the address to mail the form back. It will depend upon your state of residence.