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Tax notices arrive in a digital mailbox, and unopened notices count as served

Last verified: 2026-10-27 · Status: Stable

Abroad, tax authorities usually write to a company's address; in Mexico every taxpayer has a SAT digital mailbox (buzón tributario) through which audits, requests and assessments are served. A notice not opened within three days of the electronic alert is deemed served on the fourth day, and deadlines then run in business days, including the 30 days to appeal. Not enabling the mailbox or keeping contact details current is fined at MXN 3,850 to MXN 11,540 in 2026, lets SAT serve by public listing and can block invoicing.

USD conversions use MXN 18.6638 per US dollar, the US Federal Reserve H.10 noon buying rate in New York for 23 October 2026 (FRED series DEXMXUS), the latest observation available when this page was verified. Mexican law uses the Banxico FIX rate published in the DOF for foreign currency amounts, which differs slightly. Conversions are for orientation only.

Key facts

SAT digital tax mailbox for all RFC registered taxpayers	Mandatory textCFF art. 17-K, as of 2026-10-27 · in force
Days to open a notice after the electronic alert before it is deemed served	3 daysCFF art. 134, section I, as of 2026-10-27 · in force
Minimum fine for not enabling the tax mailbox, 2026	3850 MXNCFF art. 86-D, as of 2026-10-27 · in force
Maximum fine for not enabling the tax mailbox, 2026	11540 MXNCFF art. 86-D, as of 2026-10-27 · in force
Deadline to file an administrative appeal (recurso de revocación)	30 business daysCFF arts. 12 and 121, as of 2026-10-27 · in force

The rule

1. Every individual and company registered in the RFC has a tax mailbox on SAT's website. SAT uses it to serve any act or resolution, including ones that can be appealed, and taxpayers use it to file requests, notices and answers to requirements. Taxpayers must enable it, register and keep current their contact details, and check it within three days after receiving an electronic alert. If they do not enable it, or register wrong or outdated contacts, they are treated as opposing notification and SAT may serve by public listing.
Cost to do it: Free to use; needs the company's e.firma.
Example: A subsidiary whose registered contact address belongs to a former employee misses an SAT information request; SAT treats it as opposing notification. / No US dollar effect.Código Fiscal de la Federación (CFF), DOF 31 December 1981 (consolidated text, last reform DOF 9 April 2026), Arts. 17-K and 18, 2021-11-12 official text · verified 2026-10-27

2. Electronic service is complete when the taxpayer opens the document. The taxpayer has three days from the day after the alert to open it; if it does not, service is deemed made on the fourth day. Service takes effect on the next business day. Service by public listing means publishing the document for ten days on SAT's website, with service dated the eleventh day.
Cost to do it: No fee.
Example: SAT sends an alert on Monday 2 November 2026. If nobody opens the document, service is deemed made on the fourth day counted from Tuesday 3 November, and its effects start the next business day. / No US dollar effect.Código Fiscal de la Federación (CFF), DOF 31 December 1981 (consolidated text, last reform DOF 9 April 2026), Arts. 134, sections I and III, 135 and 139, 1981-12-31 official text · verified 2026-10-27

3. Time limits fixed in days count only business days: Saturdays, Sundays, statutory holidays and the authorities' general vacation days are excluded. An administrative appeal (recurso de revocación) must be filed through the mailbox within 30 days after service takes effect.
Cost to do it: Filing the appeal has no government fee; counsel is a separate cost.
Example: An assessment served through the mailbox must be appealed within 30 business days, about six calendar weeks, or it becomes final. / No US dollar effect.Código Fiscal de la Federación (CFF), DOF 31 December 1981 (consolidated text, last reform DOF 9 April 2026), Arts. 12 and 121, 1981-12-31 official text · verified 2026-10-27

4. Not enabling the mailbox, or not registering or updating contact details, is an infraction fined at MXN 3,850 to MXN 11,540 (2026 amounts). Contact details that are not correct or authentic, for reasons attributable to the taxpayer, are also a ground for SAT to restrict the company's seal certificate and so its ability to invoice.
Cost to do it: MXN 3,850 to MXN 11,540 per infraction (2026).
Example: A company that never enabled its mailbox is fined MXN 3,850 at the minimum and its invoicing may be restricted until it registers valid contacts. / About USD 206 to USD 618.Código Fiscal de la Federación (CFF), DOF 31 December 1981 (consolidated text, last reform DOF 9 April 2026); RMF 2026 updated amounts, DOF 28 December 2025, as printed in the consolidated CFF, Arts. 86-C, 86-D and 17-H Bis, section VIII, 2025-12-28 official text · verified 2026-10-27

Worked example

A foreign group's Mexican subsidiary is run day to day from abroad, and the mailbox alerts go to an address nobody reads.
SAT serves a request for information; the document is deemed served on the fourth day and the response period starts running in business days.
If the company misses the request and the later assessment, the 30 business day window to appeal can close without anyone in the group knowing.

Step by step

1. Enable the mailbox as soon as the RFC and e.firma are issued.
2. Register at least two monitored contacts, ideally a shared address and a mobile number held by the local finance team.
3. Assign a person to log in at least every three days and record each notice and its deadline.
4. Update contacts whenever staff or advisers change.
5. Diary every deadline in business days using CFF art. 12.

Common traps

Not opening a notice does not stop service; it is deemed served on the fourth day.
Using an adviser's contact details is fine only if the adviser actually monitors them.
Wrong contact details can restrict invoicing, not just trigger a fine.

Sources

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