Mexico’s tax authority (the SAT) no longer needs to visit your offices to audit you. Through the Tax Mailbox (Buzón Tributario) it can open a SAT electronic tax review: a fully digital procedure that is fast and shifts the burden of proof onto the taxpayer. Short deadlines start with the first notice, and the most important one gives you just 15 business days to respond. Here is how it works and how to protect your deductions.

What an electronic reviews is

The electronic review is one of the SAT’s audit powers, set out in Article 42, section IX of the Federal Tax Code (CFF), with its procedure governed by Article 53-B. Unlike a field audit, no inspectors visit your premises: everything happens through the Tax Mailbox, based on data the authority already holds —your CFDIs, tax returns and third-party information. It is the fastest-growing form of audit because it lets the SAT review taxpayers remotely and at scale.

How to procedure works

Article 53-B sets a clear sequence:

1. Provisional resolution. The SAT notifies you of the facts or omissions it found. It may attach a pre-assessment (oficio de preliquidación): an early estimate of the tax it believes you owe.

2. 15 business days. From the notice you have fifteen business days to state your case and provide documents that disprove the findings or prove payment. Within that window you may also choose to correct your situation.

3. Further requests. The SAT may ask you —or third parties— for more information within the periods the article allows, opening new terms to respond.

4. Final resolution. The authority must issue and notify the final resolution within 40 days after the periods to submit evidence end. The whole procedure is capped at six months from the provisional resolution.

All notices and your filings are handled as digital documents through the Tax Mailbox.

The 15-day clock

This is the critical deadline. If the fifteen business days pass without a response, you lose the right to disprove the findings, and the pre-assessment can harden into a final tax debt. Checking the mailbox on time is not optional.

Why your file is everything

In an electronic review there is no room to improvise: you respond with the documents you already have. A CFDI alone proves nothing about substance; you need the file that shows the transaction truly happened — contracts, deliverables, proof of performance, payments and business reason. Having that support organized and easy to retrieve is the difference between disproving on time and paying an avoidable assessment.

When a provisional resolution lands, the clock is already running. DYNAMI keeps the file for every transaction —CFDIs, contracts, proof of delivery and payments— organized and ready to respond within the 15 days, and alerts you to expired documents or suppliers listed by the SAT before the authority flags them. At Cumbre Asesores we guide companies in Mérida, Mexico City and Guadalajara through an electronic review, from the response to the provisional resolution to the final decision. If a notice reached your mailbox, let’s review it today.

Costly mistakes

• Not checking the Tax Mailbox regularly and finding out too late.
• Letting the 15 business days lapse: the right respond is lost.
• Replying with incomplete evidence that fails to prove materiality.
• Treating the pre-assessment as a mere notice.

Frequently asked questions

How long do I have to respond?

Fifteen business days from the notice of the provisional resolution.

Can the SAT charge me without hearing me?

No. It first notifies the provisional resolution and respects your defense period; the final resolution comes later.

How long does the review take?

Up to six months from the provisional resolution; the final resolution must be notified within 40 days after your evidence period closes.

Can I correct my situation?

Yes. Within the fifteen days you may self-correct, which usually reduces the penalty.