Lob Help Center

Letter envelopes

Standard letter outer envelopes

Letters printed by Lob are sent in a plain Standard #10 double-windowed outer envelope, or in a flat envelope when letter pages exceed 6 pages. These are automatically included when a Letter API request is made, and no special request will need to be made to utilize them. These standard outer envelopes cannot be customized.

Standard #10 double-windowed outer envelope 

  • Design template for standard letter & check orders (tri-folded) 
  • Fits up to 6 sheets of tri-folded paper / 12 duplexed pages
  • Paper specs:
    • Envelope face size: 4.125 x 9.5"
    • Window #1 (Top):
      • Window size: 0.875 x 3.25"
      • Position from left edge: 0.625"
      • Position from bottom edge: 2.375"
    • Window #2 (Bottom):
      • Window size: 1 x 4"
      • Position from left edge: 0.625"
      • Position from bottom edge: 1"
    • 24# White Wove
    • Contains blue inside security tint

9 x 12" single window flat outer envelope

  • Design template for standard letter & check orders (full page)
  • Fits between 7 to 60 sheets of paper / up to 120 duplexed pages 
  • Paper specs:
    • Envelope face size: 9 x 12" 
    • Window #1:
      • Window size: 4 x 3.375"
      • Position from left edge: 0.5"
      • Position from top edge: 0.625"
    • 24# White Wove
    • Contains blue inside security tint

Certified Mail envelopes

All Certified Mail printed by Lob are sent in a large single-windowed Standard #10 Certified Mail envelope with an inside security tint. These Certified Mail envelopes cannot be customized.

  • Design template for Certified single-window #10 envelope 
  • Design template for Certified letter orders (tri-folded) 
  • Fits up to 6 sheets of tri-folded paper / 12 duplexed pages
  • Paper specs:
    • Envelope face size: 4.125 x 9.5"
    • Window #1:
      • Window size: 3 x 8"
      • Position from left & right edges: 0.75" 
      • Position from top & bottom edges: 0.5625"
    • 28# White Wove
    • Contains inside security tint

Return envelopes

Lob offers two options for USPS reply mail for our letter form factors only:

  • Courtesy Reply Mail, available to all customers
  • Business Reply Mail, available to Enterprise edition customers only

Both options will require a #9 standard return envelope. To include a return envelope with your mail pieces, you will need to send a Letter API request with return_envelope and perforated_page options completed:

  • return_envelope = true, or
    return_envelope = no_9_single_window, if custom return envelopes are enabled on the account
  • perforated_page, specifying the page that will have tear-off slips with a remittance slip and return address for the reply mail

Once the return envelope setting is activated, letter designs will automatically include a bottom perforation if including a return envelope. 

Return envelopes are available to all customers by default. They are blank, come without prepaid postage, and expire in 6 months. No artwork is allowed to be printed on the front or back sides. Enterprise edition customers have the ability to further customize their artwork for no-window and single-windowed envelope options (front-side only).

Reference our design templates for where you can place your artwork, and visit our Template Gallery for inspiration.

Specs for #9 standard return envelope for letters:

  • Fits up to 6 sheets of paper / 12 duplexed pages (+ letter perforation required)
  • Envelope face size: 3.875 x 8.875" 
  • Window #1 (if single-windowed option):
    • Window size: 1.125 x 4.5" 
    • Position from left edge: 0.875"
    • Position from bottom edge: 0.5"
  • Contains inside security tint
  • Expiration: 6 months (to ensure the integrity of adhesives)

Sending Business Reply Mail (BRM)

Customers interested in sending Business Reply Mail (BRM) must use Business Return Envelopes (BREs):

  • A valid BRM permit must be obtained from USPS before you can start using a BRM mail piece and receive BRM mail
  • BRM users also need a unique Zip+4Code assigned by the USPS to qualify for volume discounts
    • Assigned Zip+4 Codes are unique to the category of Reply Mail used
  • BREs are #9 return envelopes (no windows) with inside security tint
    • A USPS-approved design must be used in BREs; no custom artwork is allowed 
    • Postage must be prepaid
    • Letter perforation is required

Note that BREs are only available to Enterprise edition customers.

Return envelope tracking

For Enterprise edition customers, Lob offers return envelope tracking for their USPS Courtesy Reply Mail services. Currently, tracking information is only available via webhooks for standard return envelopes (non-customized single-windowed envelopes only).

To access this feature, enterprise customers need to send an API request for a letter with return_envelope, return_address and perforated_page options completed:

  • return_envelope = true, or 
    return_envelope = no_9_single_window, if custom return envelopes are enabled on the account
  • perforated_page, specifying the page that will have tear-off slips with a remittance slip and return address for the reply mail
  • return_address, specifying the return address the return envelope customers should send remittance slips to

This will result in the return address and associated Intelligent Mail Barcode (IMb) tracking code to be placed within the window area of the perforated page. The #9 return envelope will be mailed to the customer along with the letter including the perforated page and return address in a #10 standard outer envelope. Note that no custom outer envelopes can be used with this feature at this time.

It is possible to send Courtesy Reply mail without enabling return envelope tracking, as they are two separate features. To use normal reply mail without tracking, make sure to skip the return_address field. This means only the return address (and no IMb) will be rendered in the window area of the perforated page. 

Tracking event notifications

Once the returned envelope enters the mail stream and is scanned by the USPS, the customer can start receiving notifications to mail tracking events, which will be surfaced via webhooks.

The following is a list of mail tracking event labels and descriptions available for reply mail:

  • Created: Return envelope is first created (should be simultaneous with Letter creation)
  • In transit: Return envelope is being processed at the entry/origin facility
  • In local area: Return envelope is being processed at the destination facility
  • Processed for delivery: Return envelope is greenlit for delivery at the end recipient's nearest postal facility. The mailpiece should reach the mailbox within 1 business day of this tracking event.
  • Re-routed: Return envelope is re-routed due to recipient change of address, address errors, or USPS relabeling of barcode/ID tag area
  • Returned to sender: Return envelope is undeliverable and is being returned to sender due to barcode, ID tag area, or address errors.

Return envelope tracking is currently only accessible via our webhooks, and the Event Logs node in the Lob dashboard. Tracking events will appear in the Letters Events portion of the original individual mailpiece in the dashboard as soon as they become available, or can be downloaded using the Export button that’s located at the top of the Letters section in the dashboard.

Additional details & best practices

Return addresses that are passed into the return_address field will be used exactly as passed in. We do not run this address through any verification services like NCOA or CASS. This helps ensure that remittance slips are sent to the business address provided. Customers must take extra care to ensure that the address information provided matches their desired delivery address.

Additionally, we recommend supplying ZIP+4 codes in the return address specified to ensure the fastest, most accurate mailing possible. This can speed up USPS processing and delivery by up to as much as 2 days.

In the future, the tracking feature will be made available for custom return envelopes and Business Reply Mail, as well as the ability to track return envelopes from the Lob dashboard.  

If you are an Enterprise edition customer looking to learn more about return envelope tracking, including specifics on pricing, reach out to our Sales team or your CSM.

Custom outer envelopes

This feature is exclusive to Enterprise edition customers. Upgrade your Print & Mail edition to gain access to this form factor, or reach out to our sales team.

Lob supports custom outer envelopes for letters only; they are not available for checks or postcards. To qualify for custom envelopes, we also require a minimum envelope order quantity of 10,000 per artwork design submitted. 

To get started with creating letters with custom envelopes, refer to our Letters API documentation or see our Template Gallery for inspiration. Custom envelopes can be created and managed in the dashboard.

Envelope dimensions & designs

Envelope dimensions & specs

Custom outer envelopes are 9.5 x 4.125" and can fit up to six tri-folded 8.5 x 11" sheets.

If you'd like to use a custom envelope with your mail piece, you will need to set the custom_envelope parameter in your POST call to https://api.lob.com/v1/letters to the desired custom envelope ID, which can be found in your dashboard. If a letter is created with a specified envelope ID that is not in stock, the letter request will be rejected. If a letter is created with a specified envelope ID and is 7+ sheets, the letter will be sent instead in a blank, flat envelope, and the custom envelope inventory will not be decremented. Additionally, custom envelopes have an expiration date, which ensures the envelope's integrity.

Specs for Standard #10 single-window outer envelope with inside security tint:

  • Fits up to 6 sheets of tri-folded paper / 12 duplex pages
  • Envelope face size: 4.125 x 9.5"
  • Window #1:
    • Window size: 1.125 x 4.5"
    • Position from left edge: 0.875"
    • Position from bottom edge: 0.5"
  • 24# White Wove
  • Expiration: 6 months (due to ensure adhesive's integrity)

Envelope designs

Reference our custom envelope template to see where you can put your design elements. 

Layout considerations

  • Bleeds should extend 0.125" past the trim line
  • Any other artwork should be 0.125" away from trim line due to movement at press
  • Custom envelopes will not be printed outside of the safe zone, nor on the flap

Accepted image submission formats

  • Preferred: PDF file (.pdf)
  • Secondary: Adobe Illustrator (.ai), Indesign (.indd), Photoshop (.psd) 

Artwork considerations

  • Outline all fonts: differences in kerning, font versions, anti-aliasing, etc., can cause small variations between what you see on your screen and what we output to press
  • Double-check that all images are embedded into your document
  • Ensure all rasterized artwork (images, effects, copy, etc.) is created and saved at or above 300 dpi
  • All images must be at or under 25% ink saturation
  • Type should be no smaller than 5 pt
  • Thin, small fonts with over 3 colors may fill in slightly or appear “fuzzy”
  • Line weights of 0.5 pt or more assure optimum print results
  • It is preferred that barcodes/QR codes are vector/editable
  • CMYK documents are preferred over RGB

Envelope window placement

The envelope window is where your recipient address information will be visible. Reference our letter template for custom envelopes to ensure that your recipient’s address is visible. No design within the envelope window will be printed.

Stamp placement

Postage will be placed in the upper right corner of the envelope. No design will be printed in this space. Refer to our custom envelope template for stamp placement.

Return address placement

USPS prefers that return addresses are placed in the upper left portion of the mail piece, on the side of the piece bearing postage. USPS does not require that all mail include a return address; however, mail sent without a return address cannot be returned.

Ordering

Envelopes must be created, ordered, printed and available in your inventory in advance before they can be utilized with Letter API call requests. These envelopes can be purchased as one-off orders or through auto-reordering directly in the Lob dashboard. The minimum order quantity for custom envelopes is 10,000 envelopes per artwork design submitted.  

  • First-time orders: Typically, any initial order process for new envelope designs can take more time for quoting, production, and shipment. Allow up to 25 days for any new design orders to be fulfilled.
  • Auto-reordering: When the auto-reordering function is turned on, a new order will be submitted whenever the remaining envelope quantity in inventory falls below 20%. A confirmation will show the reorder quantity and price that will be charged.
  • Plan ahead: Given additional lead times, we recommend enabling auto-reorder for envelopes that will be continuously utilized to ensure there will be no risk of running out.

Note: Allow an estimated 25 business days for custom envelopes to be made available in your dashboard for use. Envelopes cannot be used until the dashboard indicates that they have been made available, and any API requests including your unique envelope ID will fail. Timing and delivery is dependent on order size and complexity, and may be additionally delayed by forces outside of Lob's control.

Inventory management

Envelope details

Return to the dashboard at any given time to view existing order designs, the number of remaining envelopes, and the number of orders that are still outstanding or fulfilled. Inventory will decrease with each API call made for a specific custom envelope design corresponding to a unique envelope ID.

Auto-reorder settings

When the auto-reordering function is turned on, a new order will be submitted whenever the remaining envelope quantity in inventory falls below 20%. A confirmation will show the reorder quantity and price that will be charged.

Given that custom envelopes have additional lead times, we recommend enabling auto-reorder for envelopes that will be continuously utilized to ensure there will be no risk of running out.

Order history

View previously submitted orders, and order details once any order is submitted. Rough expected date of availability for submitted orders provides an approximate time of when envelopes may be available, while an email confirmation will be sent when envelopes are actually ready for use.

Custom letter envelopes are set to expire in 6 months (due to adhesives). Expiration dates of ordered designs that still remain in your inventory can be viewed. Once envelopes are expired, customers will not be able to access any remaining inventory of the particular design order in their dashboard.

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