Keeping your tax situation under control is the best way to avoid unpleasant surprises from the SAT. This includes enabling the Tax Mailbox, as it is mandatory and subject to fines.

However, many taxpayers don’t know they must activate it or what the process entails. If that’s your case, read this post to discover everything from the minimum requirements to the step-by-step process for enabling your Tax Mailbox in 2025.

SAT Tax Mailbox: What It Is and How to Activate It to Avoid Fines

What Is the SAT Tax Mailbox?

It is a service offered by the Mexican Tax Administration Service (SAT) to communicate directly with taxpayers. A secure and fast channel designed so you don’t have to visit an office.

The idea is to make it easier to receive official notifications and send messages related to tax procedures. But these are not the only benefits of the Tax Mailbox; it also:

• Is a private channel that allows you to manage procedures in one place.

• Saves time and resources.

• Lets you receive official notices anytime, anywhere.

• Helps you check if there are fines or outstanding debts with the SAT.

• Records SAT resolutions and actions within the system.

• Is used to send you details about available programs you may take advantage of.

In short, it is a useful tool to stay up to date with your tax obligations. At the same time, it protects your data and ensures the communications are genuine, not fraudulent.

Who Must Have a Tax Mailbox?

Activating the SAT Tax Mailbox has been mandatory since 2020 for most Mexican taxpayers. This applies to both legal entities and individuals.

Therefore, if you are registered with the RFC and have active tax obligations, you are most likely required to activate it.

However, there are cases where it is not mandatory or is optional:

If you do not fall under one of the exceptions mentioned above, you are required to activate the Tax Mailbox. Fortunately, the SAT has announced an extension until December 31, 2025, to enable it if you haven’t done so yet.

What Happens If I Don’t Activate My SAT Tax Mailbox?

Failing to enable your Tax Mailbox is grounds for a penalty.

Articles 86-C and 86-D of the Federal Tax Code state that:

• Sanctions apply both for not activating the Mailbox and for failing to update your contact methods (email or mobile number).

• The fine ranges from $3,080 to $11,540 MXN, slightly lower than the penalty for not updating your tax address in the RFC.

Keep in mind that you must enable it no later than two months after submitting a notice to the SAT regarding:

• Registration in the RFC to pay taxes under RESICO.

• Resuming activities (if you were suspended).

• Updating your economic activity in the RFC.

For example, suppose you register with the RFC as RESICO in August 2025. This means you have until October 31, 2025, to enable your Tax Mailbox.

This is the deadline to enable the Tax Mailbox under RESICO (p. 518).

How to Activate Your Tax Mailbox (Step by Step)

To walk you through the steps for enabling your SAT Tax Mailbox, you first need to know what you’ll need:

• e.firma if you are registered as a legal entity.

• Password, electronic signature (e.firma), or portable e.firma if you are an individual.

• Active email address and mobile phone number.

If you have these, follow these steps:

1. Access the SAT

Go to the official SAT website and head to the Tax Mailbox section to log in, or click here. There, you must enter your RFC, the authentication method of your choice (password or e.firma), and the captcha.

2. Register Your Contact Information

Next, you’ll be asked for your contact details, including your phone number and email address (you can add up to 5 email addresses).

Make sure they are typed correctly.

Once you finish entering your information, a receipt will be generated with the date, time, and tracking number. You can download and print it to keep as proof.

3. Confirm the Information Entered

You will receive a text message at the registered phone number with a code and a confirmation link via email. You will use both to validate each channel as follows:

• Log back into the portal, access your Tax Mailbox, and enter the code received via SMS.

You will have 3 attempts to do this correctly. If you make mistakes all 3 times, the system will lock for 30 minutes.

• Check your email and click the verification link that was sent to you. This step is equally important for the mailbox to be activated.

NOTE: The system gives you up to 72 hours to validate the data from the moment you receive the code and SMS.

How to Check Notifications and Avoid Additional Fines

Once you activate your Tax Mailbox, you should check it frequently to avoid any penalties. As we mentioned, it is the SAT's official means of sending you notices, requests, or resolutions. For example, notifications of fines for transfers or for filing your return late.

To check your notifications in the Tax Mailbox, simply:

• Go to www.sat.gob.mx and select “Tax Mailbox” from the main menu.

• Access the mailbox with your RFC and password, or with your e.firma.

• Once inside, look for “Notifications” or “SAT Messages” to view the available documents.

On the site, you will also find an option for “My Procedures and Services”, which allows you to:

• Submit documentation.

• View promotions.

• Make inquiries.

You can also track the paperwork you have already submitted.

What to Do If I’ve Already Been Notified or Fined?

The SAT system can be strict, but it also helps you regularize your tax situation—from recovering certificates to taking quick action in case of fines.

The important thing is not to ignore any notification you receive in the Tax Mailbox:

• Locate the message informing you of the infraction or sanction after logging in.

• Read the description of the fine, its legal basis, and whether you have the option to clarify or pay it.

• Verify the reason and amount of the fine (for example, not enabling the mailbox or not updating your contact information). Take note of the tracking number, payment deadline, and exact amount.

• Submit a clarification if you believe it was incorrect by going to “Services” → “Clarifications.”

• If the fine applies, generate your payment reference directly from the Tax Mailbox message and proceed with payment.

Extra Tip: Activate alerts and make it a habit to check the mailbox at least once a week.

Ignoring or disregarding messages received from the SAT could result in fines or penalties. In some cases, it could lead to more serious consequences, such as a cabinet review.

Conclusion

The Tax Mailbox is your direct line of communication with the SAT and a tool that helps you keep your tax situation under control—whether by preventing the loss of important notices, safeguarding tax benefits, or, of course, avoiding fines.

In addition, it is a legal obligation like any other, so we suggest making it part of your regular tax routine. In any case, it won’t take much time to check the site, keep it active, and ensure your information is up to date. So, if you haven’t activated it yet, do it before the end of the year to avoid putting your finances at risk.

DolarApp is also a useful tool to protect your finances if you manage money in another currency—especially if you want to handle U.S. dollars or euros—since we offer a digital account to make such transactions easier.

Our app operates with USDc and EURc, allowing you to send or receive money from abroad. We also provide a fair exchange rate for when you need to move your money between the different available currencies.

Download it and take advantage of its benefits!

Frequently Asked Questions

What if I already have an email or phone number registered?

You must log in to the SAT portal and revalidate both pieces of information. Confirming your contact methods is essential for your Tax Mailbox to be enabled properly.

Can I avoid the fine if I activate the mailbox after the deadline?

If you haven’t activated it by January 1, 2026, the SAT will apply the fine established in the Federal Tax Code. Activating it late does not automatically eliminate the sanction, although it could help you avoid them in the future.

Is it possible to activate the Tax Mailbox without an e.firma?

Yes. If you are registered as an individual, you can enable it using your RFC and SAT password. If, on the other hand, you are registered as a legal entity, you must do so with a valid e.firma.