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. It 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

Go to the Sidr Tax Autofile page and complete the Business Information section (business name, Federal EIN or SSN, entity type, business representative, and addresses). We use this information to provision your mailbox. If you are setting up Autofile anyway (and we recommend you do) this step is already part of that setup (see How to setup Sales Tax Autofile).

3. Complete USPS Form 1583

USPS Form 1583 is a federal requirement that authorizes our mail facility to receive mail on your behalf. Sidr Tax pre-fills the form for you; you only need to provide two documents:

• a photo ID (such as a driver's license or passport)
• a proof of address (such as a lease, insurance policy, or vehicle registration)

Then sign it electronically. No notarization is required, and international documents are accepted.

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.

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.

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

Updated on: 07/07/2026