R.I. Gen. Laws § 44-1-28 — Mailing as timely tax filing and payment

(a) Generally. Any report, claim, tax return, statement, or other document required or authorized
to be filed with or any payment made to the state or to any political subdivision
of the state which is:
(1) Transmitted through the United States mail, is deemed filed and received by the state
or political subdivision on the date shown by the post office cancellation mark stamped
upon the envelope or other appropriate wrapper containing it;
(2) Mailed but not received by the state or political subdivision or where received and
the cancellation mark is illegible, erroneous, or omitted, is deemed filed and received
on the date it was mailed if the sender establishes by competent evidence that the
report, claim, tax return, statement, remittance, or other document was deposited
in the United States mail on or before the date due for filing; and in cases of the
non-receipt of a report, tax return, statement, remittance, or other document required
by law to be filed, the sender files with the state or political subdivision a duplicate
within thirty (30) days after written notification is given to the sender by the state
or political subdivision of its non-receipt of the report, tax return, statement,
remittance, or other document.
(b) Registered or certified mail; Certificate of mailing. If any report, claim, tax return, statement, remittance, or other document is sent
by United States registered mail, certified mail, or certificate of mailing, a record
authenticated by the United States post office of the registration, certification,
or certificate is considered competent evidence that the report, claim, tax return,
statement, remittance, or other document was mailed, and the date of registration,
certification, or certificate is deemed the postmarked date.
(c) Saturdays, Sundays and legal holidays. If the date for filing any report, claim, tax return, statement, remittance, or other
document falls upon a Saturday, Sunday, or legal holiday, the filing is considered
timely if performed on the next business day.