N.M. Admin. Code § 11.3.100.101
Any report, response or other document required to be filed by the Unemployment Compensation Law or these rules, and any appeal, notice or other pleading required to be filed with the department shall be deemed filed on the date it is received by the department or, if mailed, as of the date of the postmark on the envelope. If it is postmarked at or prior to the deadline, it will be deemed filed timely if received by the department within a reasonable period of time. Unless otherwise specified by law or rules any report, response document or appeal that is mailed but has no postmark date shall be considered timely if, on the basis of customary mail practice and the actual date of delivery, it may be presumed to have been mailed within the specified time period. If the final day for a report, response document or appeal falls on a date when the department offices are closed, receipt on the first business day thereafter shall be considered timely.
N.M. Admin. Code § 11.3.100.101