Frequently Asked Questions

Lob's API documentation is designed to be completely self-serve, but that doesn't mean we don't love hearing from you. If you can't find what you're looking for, we're here to help. Take a look at the FAQs below, send us an email or a tweet, and we'll get back to you well within 24 hours.

Lob Basics

What product specs for letter envelopes do you have available?

Standard Double Window Envelope Specs

  • #10 Blank Double-Window Envelopes with Inside Security Tint
    24# White Wove
  • Fits up to 6 Sheets of Paper / 12 Duplex Pages

Flat Envelope Specs

  • 10" x 13" Blank Envelopes with Inside Security Tint
  • 24# White Wove
  • Accommodates 7 Sheets of Paper+

Letters and checks will be mailed in a standard double window envelope. Letters over 6 pages single-sided or 12 pages double-sided will be placed in a flat envelope instead.

How can I edit an address?

You cannot edit any existing addresses via the dashboard or API request. You can delete the current address and add a new one with the updated fields. For more information on adding a new address please refer here.

How can I re-invite a deleted user to my account?

Please reach out to support via email at to re-invite a deleted user.

Is there a way to upload a CSV of my address list and documents?

Lob currently does not offer a method to bulk upload addresses or mailings via the Lob dashboard. If you are looking for a tool to use our service without integrating with our API directly, we encourage you take a look at our various integrations and partner applications.

How long do micro deposits take to hit my account?

Typically, micro deposits take between 2-3 business days to hit your bank account.

Where can I find my Account ID?

You can find your Account ID through the following steps:

  1. Log into your dashboard
  2. Click on the Settings tab on the top right corner


  3. You’ll find your Account ID under the Account tab


What can I do with Lob?

Lob's API products empower technology-focused companies to build powerful applications to control and scale their physical mailing. Instead of working through the complexities of direct mail, you can now access commercial grade printing & mailing infrastructure on-demand via a simple RESTful API.

What kind of companies use Lob?

Lob's customers range from Fortune 500 companies all the way to single developers working on side projects.

Whether you are sending one piece of mail or millions, Lob's products are built to be affordable and easy-to-use.

How can I start mailing?

Integrating with Lob is easy! You can start mailing by following the steps below:

  1. Sign up for an account.
  2. Start with our Getting Started Guides.

Can I track my mail?

Each First Class postcard, letter, and check sent through Lob has a unique IMb barcode that gets scanned by USPS as it travels through the mail stream. You can access this scan event data via our API or Dashboard, or get notifications for them by creating webhooks. Below is a breakdown of each scan event label and description:

  • In Transit - The mailpiece is being processed at the entry/origin facility.
  • In Local Area - The mailpiece is being processed at the destination facility.
  • Processed for Delivery - The mailpiece has been greenlit for delivery at the recipient's nearest postal facility. The mailpiece should reach the mailbox within 1 to 2 business days of this scan event.
  • Re-routed - The mailpiece is re-routed due to recipient change of address, address errors, or USPS relabeling of barcode/ID tag area.
  • Returned to Sender - The mailpiece is being returned to sender due to barcode, ID tag area, or address errors.

For First Class Mail, you will usually see your first scan event around 3 business days after the piece has been scheduled to go out.

Please note that IMb tracking data cannot be accessed via USPS's website and IMb tracking data not available for the following products:

When should I expect to start seeing tracking events?

Tracking events typically start appearing at earliest 3 mailing days after sending your API request (and in some cases can take longer). Please note that IMb scans are not guaranteed by USPS, but we do see scans on over 99% of our mailings.

Does international mail receive tracking events?

International mailings will typically receive an "In Transit" scan, indicating that the mailpiece has been processed at the entry/origin facility. However, because delivery occurs in a foreign country outside of the control of USPS, international mailings do not receive scans beyond that.

What do I do if I receive a "Re-routed" scan event?

If you receive a "Re-routed" scan, this indicates that USPS attempted delivery at the original address, but re-routed it because your recipient no longer resides at that address. In these cases, USPS will attempt to deliver to your recipient at their new address (if they filed a Change of Address).

What do I do if I receive a "Returned to Sender" scan event?

If you receive a "Returned to Sender" scan, this indicates that USPS attempted delivery at the original address, was unsuccessful, and the mailpiece is being sent back to the return address. In these cases, the address you mailed to was invalid. Please reach out to your intended recipient to update the address.

When will tracking for my Certified/Registered/Overnight mailing be available?

Letters sent as certified or registered and checks sent as overnight will not receive IMb scan events listed above. Instead, a carrier tracking number will be assigned when it becomes available 3 business days after the API request is received. A tracking number will not be populated for letters or checks created in test mode.

Where are my API Keys?

Your API Keys can be found in the "API Keys" tab of your Settings.

What is the difference between my test and live API Key?

Requests sent with your test API key will not be actually printed/mailed. Use your test API key to try out the functionality of our service without worrying about being charged. Requests sent with your live API key will actually be printed and mailed.

How long until my mail is delivered?

Delivery times will vary depending on product and destination. Domestic delivery times are listed below:

  • Letters - 4 to 6 business days
  • Postcards - 4 to 6 business days
  • Area Mail - 6 to 10 business days
  • Checks - 4 to 6 business days

International mailings will take an additional 5 to 7 days.

*Delivery times above are estimates; Lob uses USPS as our primary carrier and USPS experiences delays from time to time. To see the most up-to-date status of your mailing, check the tracking information of your particular mailing through a GET request or on your Dashboard.

How can I invite other people to my account?

You can invite team members from the "Team" tab of your Settings.

What do the different permission levels give access to?

When inviting team members, there are three possible permission levels to choose from:

  • Administrator gives unrestricted access to everything. You can see API keys, update payment information, invite new users and edit existing users, etc. By default, the first creator of the Lob account is an Administrator.
  • Read & Write lets users use the API and view past API requests, but does not allow access to certain account information. Read & Write users cannot view or update payment information, change pricing plans, edit or delete other team members, or edit company information.
  • Read Only only lets users view past API requests. Read Only users cannot see API keys, create test or live API requests, upgrade your API Version, view or update payment information, change pricing plans, edit, delete, or invite other team members, or edit company information.

Can I get a sample?

The best way to see what our products look and feel like is to send one to yourself! This way you will also get to see how the API works end-to-end.

Will my mailings be delayed due to my cancellation window?

Yes, the cancellation window on your account will delay the sending of all postcards, letters, and checks by the desired window. So if you want to meet a daily cutoff of 11AM and your cancellation window is 60 minutes, your cutoff time is actually 10AM. If you'd like to bypass your cancellation window for a certain send, you can do so by scheduling your mailing.

Can I apply different cancellation windows to different products?

You can modify your cancellation window for postcards, letters, and checks individually in your Dashboard Settings. Keep in mind that any changes submitted on this page will only apply to mailings sent afterwards, not mailings that have already been submitted.

What other services do you integrate with?

There are a number of third party tools that you can use to leverage our API. Below are a few:

  1. Zapier
  2. Mailform
  3. Webmerge

Is Lob available outside of the US?

Lob can mail all over the world. International mailings originate from the US and are mailed via USPS First Class Mail.

If you are looking to originate mail in a different country, please contact us.

Do you change or cleanse the addresses we mail to?

We do cleanse your addresses in order to optimize for maximum deliverability. If you are on API Version 2017-08-14 or above, all US addresses created through POST /v1/addresses and all inline addresses created through POST /v1/postcards, POST /v1/letters, and POST /v1/checks will be automatically standardized, cleansed, and verified through our CASS-Certified Address Verification system before being returned back to you in the API response. All international addresses will simply be standardized by being transformed to all uppercase. Afterwards, postcards and letters will be run through NCOA (National Change of Address), as these are requirements for sending USPS First Class Mail. This may result in the final mailing address being different from the ones you see in your API requests and Dashboard.