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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 by default.

Standard #10 outer envelope (double-windowed)

  • 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
  • Fits up to 6 sheets of tri-folded 8.5 x 11" paper / 12 duplexed pages

9 x 12" Flat outer envelope (single window)

  • 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
  • Fits between 7 to 60 sheets of 8.5 x 11" paper / up to 120 duplexed pages

Certified Mail envelopes

This feature is exclusive to higher edition customers. Upgrade your Print & Mail edition to gain access to this form factor, or reach out to our sales team to learn more.
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.
  • 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
  • Fits up to 6 sheets of tri-folded 8.5 x 11" paper / 12 duplexed pages

Return envelopes

This feature is exclusive to higher edition customers. Upgrade your Print & Mail edition to gain access to this form factor, or reach out to our sales team.
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 reply mail options will be sent in a standard #9 return envelope (single-windowed), which are available to all customers by default. They are blank, come without prepaid postage, and will expire in 6 months. No custom artwork is permitted on the front or back sides of these plain #9 envelopes. See our Template Gallery for design examples.
  • Envelope face size: 3.875 x 8.875"
  • Window #1:
    • 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)
  • Fits up to 6 sheets of 8.5 x 11" paper / 12 duplexed pages (+ letter perforation required)
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
  • 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.
For customers who want to further customize their #9 envelope artwork, send Business Reply Mail, or track return envelopes, these advanced features are available to Enterprise edition customers. See the Custom Envelope section below to learn more about custom artwork envelopes, or contact our sales team for further detail.

Sending Business Reply Mail (BRM)

Enterprise-edition 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

Return envelope tracking

For Enterprise-edition customers, Lob offers return envelope tracking for their USPS Courtesy Reply Mail services. Return tracking information is only available via webhooks for standard return envelopes (non-custom 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 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.
Note: As USPS does not return the Delivered mail tracking event for return envelopes, Lob is unable to surface this event via webhooks.

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.

Custom envelopes

Customizing envelope artwork is a feature exclusive to Enterprise edition customers. Upgrade your Print & Mail edition to gain access to this feature, or contact our sales team.

Overview

Lob allows customization of select #10 outer envelopes and #9 return envelopes. Envelopes must be created, ordered, printed and made available in your inventory before they can be utilized with Letter API call requests. Envelope orders and inventory can be fully managed in the Lob dashboard. Note that custom envelopes are only supported for letters, and are unavailable for checks or postcards.
To start creating letters with custom envelopes, refer to our Letters API documentation or see our Template Gallery for inspiration.

Envelope dimensions & specs

Standard #10 outer envelope (single-window only)

  • 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
  • Contains inside security tint
  • Expiration: 6 months (due to ensure adhesive's integrity)
  • Fits up to 6 sheets of tri-folded 8.5 x 11" paper / 12 duplex pages

Standard #9 return envelope (no-window & single-window options)

  • 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)
  • Fits up to 6 sheets of tri-folded 8.5 x 11"paper / 12 duplexed pages (+ letter perforation required)

Design placement

Follow the guidelines below to achieve optimal results for your envelope designs, and to ensure a smooth creation process.
  • 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
  • Preferred: PDF file (.pdf)
  • Secondary: Adobe Illustrator (.ai), Indesign (.indd), Photoshop (.psd)
  • 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
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.
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.
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

Envelopes must be created, ordered, printed and available in your inventory before they can be utilized with Letter API call requests.
First, create an envelope design by uploading your artwork in the 'Envelope' section of the Lob dashboard. Hit “create”, and in the new envelope creation screen, select the envelope size & design and the desired postage option for #10 outer envelopes. Any #9 return envelope selection will default to USPS Standard Class postage.
#10 custom outer envelopes (front & back options)
#9 custom return envelopes (front-side only)
Once envelope designs are uploaded into the dashboard, an order must be placed to make them available in your inventory for later use. Envelopes can be purchased as one-off orders or through auto-reordering directly in the Lob dashboard.
  • 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.
    • The minimum order quantity for any custom envelope order is 10,000 envelopes per artwork design submitted.
    • It is strongly recommend to add 3% to all order quantities to account for any spoilage during the production process.
  • 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.
    • Additionally, custom envelopes have a 6-month expiration date to ensure the adhesive's integrity. Any unused envelopes that have expired will be discarded by Lob.
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 preemptive API requests that include your unique envelope ID will fail.

Sending letters with custom envelopes

Once an envelope order is available in your inventory, it can now be utilized with Letter API call requests.
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.
When using the single endpoint Letter API, the minimum quantity of envelopes that can be sent during any 24-hour production-day period (10AM PT - 10AM PT) is 4,000 envelopes. For any customer that fails to send over the 4,000 envelope minimum (with corresponding Letter API calls) will incur a flat surcharge of $375/day on your month-end usage invoice.
Reach out to your dedicated Customer Success Manager if you have any questions.

Inventory management

Envelope details

Return to the dashboard at any given time to view existing order designs, the number of remaining envelopes, the number of orders that are still outstanding or fulfilled, and mailing class/postage type selected. 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.