Sidr Tax Virtual Mailbox: Overview and Setup

The Virtual Mailbox is how Sidr Tax turns your sales tax compliance into full automation. It gives your business a dedicated physical mailing address and a dedicated email address that Sidr Tax registers with state tax agencies on your behalf, so that state communications come straight to us, and we can acknowledge, act, and respond immediately.

The Virtual Mailbox is included at no additional cost with the Standard and Premium plans.

What is the Virtual Mailbox?

When you activate the Virtual Mailbox, Sidr Tax provisions two addresses that are unique to your business:

1. A physical mailing address — a real street address (not a P.O. box) with a suite number unique to your business. Here's an example:

2261 Market St
Suite ____
San Francisco, CA 94114

Any physical mail sent to this address is securely opened, scanned, and delivered to your Sidr Tax Inbox, where both you and the Sidr Tax team can see it the moment it arrives.

2. A group email address — an address on our domain that is unique to your business, for example acme-inc@sidrtax.com for a company called Acme Inc. Emails sent to this address are delivered to both your team and the Sidr Tax team at the same time.

Sidr Tax registers these addresses with any state where you are registered or registering, so state Departments of Revenue send their correspondence (notices, PIN letters, filing frequency changes, audit inquiries, and everything else) directly to your Virtual Mailbox.

Why does it matter?

State tax agencies still rely heavily on postal mail and email to communicate important, time-sensitive matters. Without the Virtual Mailbox, that mail goes to your own business address, and your sales tax experience is only partial automation: Sidr Tax files and remits for you, but you still need to watch your own mailbox and manually forward every state letter or email to us before we can act on it. A notice that sits unopened for a few weeks can turn into penalties and interest.

With the Virtual Mailbox, Sidr Tax has full visibility into every state communication the moment it arrives. We immediately acknowledge it, take action, and respond to the state if a response is needed, without waiting on a forward from you. This significantly reduces the chance of penalties and interest caused by late action, and it is what makes Sidr Tax full automation: registration, calculation, filing, remittance, and state correspondence, all handled end to end.

What you can expect

• Immediate notification: you are notified as soon as any physical mail or email is received.
• Full visibility into every message: you can open a scan of every piece of physical mail, and the original email for anything sent to your group email address, at any time in your Sidr Tax Inbox.
• Full visibility into every action we take: for each item, you can see how Sidr Tax responded: what we acknowledged, what we filed or corrected, and what we sent back to the state.
• Fewer penalties and interest charges: because state matters are handled immediately instead of waiting in a mail pile.
• A truly hands-off experience: no more forwarding scans and emails to your tax provider.

How it works

• Sidr Tax registers your Virtual Mailbox addresses with each state as your mailing address and contact email. We can use them for new registrations as well as update them on your existing state accounts.
• When a state sends physical mail, our secure mail facility receives it, scans it, and delivers the scan to your Sidr Tax Inbox. When a state sends an email to your group address, it is delivered to your team and ours simultaneously.
• The Sidr Tax team reviews every item, acknowledges it, takes the required action (for example, updating your filing frequency or responding to a notice), and records the resolution so you can follow along.
• You are notified immediately when mail arrives, and you can review both the message and our response in the Inbox page of your Sidr Tax account.

How to set up the Virtual Mailbox

1. Subscribe to the Standard or Premium plan

The Virtual Mailbox is included at no additional cost with any full-priced Standard or Premium plan. Go to the Subscriptions page in your Sidr Tax account and select your plan.

To learn more about plans, review this article: Sidr Tax Pricing and Subscription Plan Overview.

2. Fill out your general business information and registration information

Go to the Sidr Tax Autofile page and complete the Business Information section. We use this information to provision your mailbox and pre-fill your USPS Form 1583, so it is important that it is accurate and up to date.

We recommend that you complete the full Business Information section. Specifically, the following field is needed for your Virtual Mailbox postal address:

• Business Name

Then go to the Sidr Tax Registrations page and complete the Registration Information section. We use this information to provision your mailbox and pre-fill your USPS Form 1583, so it is important that it is accurate and up to date.

We recommend that you complete the full Registration Information section. Specifically, the following fields are needed for your Virtual Mailbox postal address:

• Incorporation State. For domestic companies this should be the county and state; for international companies it should be the country.
• At least one business owner in the Business Owner(s) section. This should be an officer of the company and is the person who will sign the USPS Form 1583. In particular, the Virtual Mailbox postal address requires:
• Full name
• Title or role at the company
• Email address
• Phone number
• Address (this cannot be a Registered Agent address, and it should appear on a document you upload)

If you are setting up Autofile and Registrations anyway (and we recommend you do), these steps are already part of that setup. See How to setup Sales Tax Autofile and How to setup Sales Permit Registration.

3. Complete USPS Form 1583 online

USPS Form 1583 is a federal requirement that authorizes our mail facility to receive mail on your behalf. It is called the Application for Delivery of Mail Through Agent, and it is a compliance document that holds agents and their customers accountable for the proper use of a postal mailing address in the United States.

Navigate to the Virtual Mailbox and under the "Postal" tab, click the "Setup" button:

Sidr Tax pre-fills the form for you using the business information you provided in step 2, then generates a secure, hosted signing link that is unique to you. The link is the USPS Form 1583, pre-filled with your information. When you open it, you will:

1. Review your pre-filled business and signing officer information.
2. Upload a primary government-issued ID. Accepted types include:

   
   

   
   

   
   Upload clear, legible photos of the front and back in JPG or PNG format.
3. • Passport
   • U.S. state driver's license or ID
   • Certificate of naturalization
   • Matrícula Consular
   • NEXUS card
   • Uniformed service ID
   • U.S. Access Card
   • U.S. permanent resident card (green card)
   • University ID with your name and photo
3. Upload a secondary ID that shows your address. Accepted types include:

   
   

   
   This serves as proof of your physical address.
4. • U.S. state driver's license or ID (if not already used as your primary ID)
   • Current lease or rental agreement
   • Home or vehicle insurance policy
   • Mortgage deed or property title
   • Vehicle registration
   • Voter card
   • Utility bill (gas, electric, or water)
4. Review and digitally sign the form. Once you sign, the form is submitted to Stable for processing.

No notarization is required, and international documents are accepted (see the translation requirements in the FAQ below).

Note: Your signing link is valid for about 30 days. If you do not complete the form within that time, the link expires and you will need a new one.

4. We provision and register your addresses

Once your form is verified, Sidr Tax provisions your unique physical mailing address and group email address, and begins registering them with your states. From that point on, your state correspondence is on full automation. You can view everything from the Inbox page in your Sidr Tax account.

What happens after you sign

After you complete and sign the USPS Form 1583, your mailbox moves through the following stages:

You will receive email notifications to the signing officer email on file, and you can see confirmation in the Inbox page of your Sidr Tax account.

After setup

Once your Virtual Mailbox is set up:

1. Verify your addresses appear in your Sidr Tax account.
2. Check the Inbox page to confirm mail and email delivery.
3. Review any state correspondence and Sidr Tax responses.

Your mailbox becomes active once Stable completes verification of your USPS Form 1583, which typically takes 3–5 business days after you sign. You will be notified by email when your address is live.

Troubleshooting

USPS Form 1583 verification failed

Ensure your photo ID and proof of address are clear and legible. International documents are accepted, but must be in English or accompanied by a certified translation.

My signing link expired

Your signing link is valid for about 30 days. If it expires before you complete the form, contact support using the green chat button in the app and we will generate a new link for you.

Not receiving mail or email notifications

Verify that the Virtual Mailbox is activated in your Sidr Tax account. Check the Inbox page for any pending items. Contact support if notifications are not appearing.

FAQ

How much does the Virtual Mailbox cost?

It is included at no additional cost with the full-priced Standard and Premium plans.

Is the Virtual Mailbox required?

No, but we strongly recommend it. Without it, you must monitor your own mailbox and email, and forward every state communication to us yourself, which means your compliance is only partially automated and slow forwarding can lead to penalties and interest. With the Virtual Mailbox, Sidr Tax handles state correspondence end to end for full automation.

Can you use the addresses for states where I'm already registered?

Yes. Sidr Tax can register your Virtual Mailbox addresses with any state. We use them for new registrations and can update the mailing address and contact email on your existing state accounts.

Will I still be able to see my mail?

Always. You have full visibility into every message: a scan for physical mail and the original email for messages sent to your group email address, plus full visibility into every action Sidr Tax takes in response. You are notified immediately whenever mail is received.

Does the physical address replace my business address?

No. It is a dedicated mailing address for state tax correspondence only. Your registered business address stays the same.

What is Stable and what role does it play?

Stable is the provider of the physical mailing addresses used for the Virtual Mailbox. It is a Commercial Mail Receiving Agency (CMRA) that provides the street addresses and remote mail handling services such as scanning and forwarding postal mail. The USPS Form 1583 is signed directly between you and Stable; Sidr Tax facilitates the process but is not a party to the form.

Why is my Virtual Mailbox address in Wilmington, Delaware?

Sidr Tax uses a single Wilmington, DE location for all customers to keep the setup simple and reduce the number of decisions you need to make. We researched the available locations and selected Wilmington, DE because it carries the least risk of being mistaken by a state or locality as creating a physical nexus for your business.

When do I get access to my address?

You get access to your address after the USPS Form 1583 is completed (your IDs uploaded and the form signed) and counter-signed by Stable, which usually takes another 1–3 business days. The address is technically created before you sign, but it cannot be provided to you until the 1583 process is cleared.

I'm a foreign company or foreign national. Can I still set up the Virtual Mailbox?

Yes. There is no restriction on foreign companies or foreign nationals acquiring an address through a CMRA. However, there are additional requirements that may apply, mainly around document language:

• All documents submitted must be in English, or accompanied by a certified translation as defined by USPS Form 1583.
• Acceptable certified translations include a translation by a USCIS-recognized translator, a professional certified translator with credentials, a notarized statement of accuracy by the translator, with the translator's contact information and a statement that the translator is not affiliated with you.
• We recommend RushTranslate for certified translations. Their services are affordable, have a track record of being accepted across USCIS agencies, and typically have a 24-hour turnaround.
• When a translation is required, upload both the original non-English document and the certified translation to the form.

Can the signing officer's address be a business address instead of a home address?

Yes. It is common for privacy reasons to list an officer's address as the same as the company's business address. However, this address must match what is submitted for the secondary ID.

Best practices

• Activate the Virtual Mailbox as early as possible to avoid missed state correspondence.
• Complete your USPS Form 1583 promptly — your signing link is valid for about 30 days.
• Review the Inbox page regularly for new mail and Sidr Tax responses.
• Ensure your USPS Form 1583 is submitted promptly to avoid delays in address provisioning.
• Keep your payment method current on the Subscriptions page to avoid service interruptions.
• Contact support using the green chat button in the app if you have questions about your Virtual Mailbox.

If you have additional questions, you can always chat with us in-app, or email us at support@sidr.io.

Updated on: 08/20/2026