Missouri recently announced through their Withholding Tax FAQs that employers with more than 250 employees must file their W-2 forms with Form MO W-3 electronically by January 31, 2018 (for tax year 2017). This announcement advances the due date for W-2 filing by one month to bring the MO due date in line with the federal deadline.
For additional information on Withholding Tax filing obligations, and to view this specific update, please visit the Missouri Withholding Tax FAQs page here (see section titled “Paperless Reporting, Compact Disc or Flash Drive – Is Paperless Reporting of W-2 data voluntary or mandatory?”).