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Letters

What it is​

Letters are 8.5×11-inch mailers sent in envelopes. Two formats are available:

  • Windowed letter - the recipient's address shows through a transparent window cut into the envelope.
  • Windowless letter - no address window; the address is printed on the envelope directly.

Both formats mail in a standard US business envelope (#10, 4.125″ × 9.5″). The envelope size is fixed and cannot be changed.

Both formats support two send modes:

  • Handwritten Cover Letter (cover page mode) - your message printed in handwritten-style font on a cover page, over an optional background design. You can optionally attach additional pages as a PDF appended after the cover. Additional pages can be printed front/back.
  • Upload Full PDF (PDF-only mode) - the entire mailer is a PDF you upload. There is no handwritten cover page; your PDF is the complete letter. All pages can be printed front/back.

You choose the mode on the Letter step of Send Mail, or on the Writing step when you make a letter creative.

Both formats support Standard and First Class postage and replacement variable personalization.

When to use it​

  • Formal communications where a traditional letter format builds credibility (B2B, legal notices, nonprofit appeals)
  • Long-form content that needs more space than a postcard - proposals, newsletters, multi-page donor letters
  • Situations where the envelope presentation matters: windowed letters look like official mail and get opened
  • Nonprofit fundraising appeals and donor acknowledgments

Windowed letters​

For windowed letters, thanks.io prints each recipient's name and address in the window zone, the upper-left area of page 1 that shows through the envelope window. You never add the address yourself. The design previews in Creatives and Send Mail draw the envelope window over your letter.

  • Leave the window zone blank. Don't put an address, logo, or any other design element there - anything in that area gets printed over or shows through the envelope window.
  • Use a white or light background behind the address area.

In cover page mode, the window zone is on the cover page, and thanks.io keeps it clear for you. In PDF-only mode, your PDF is the entire letter, so page 1 of your PDF must leave the window zone blank. Don't include the recipient's address in your PDF. thanks.io prints it for you, and an address already in the PDF ends up with a second address printed on top of it.

Windowless letters​

Windowless letters have no window constraint - full design freedom across the entire letter. The address is handled separately by the printing process. Windowless letters are mailed with a real postage stamp, and the recipient's address is printed on the envelope in a handwriting font. The envelope color cannot be modified.

Use the windowless format when:

  • Your design spans the full page without an address zone.
  • You're sending a newsletter or multi-page document as a PDF.

Send modes​

Both windowed and windowless letters support the same two send modes.

Cover page mode (Handwritten Cover Letter)​

Your first page is a cover with your message in handwritten-style font, printed over a background design. The background is optional: pick a letter creative, choose or upload a background on the Design step, or leave it empty for the plain letter background. You can optionally attach additional pages as a PDF (up to 10 pages) appended after the cover, on the Extra Pages step. Additional pages can be printed front/back.

PDF-only mode (Upload Full PDF)​

Your entire mailer is a PDF you upload (8.5 × 11, up to 12 pages and 30MB). There is no handwritten cover page - your PDF is the complete letter. All pages can be printed front/back. This is the right mode for newsletters, CMA reports, multi-page proposals, and any document that already exists as a formatted PDF file.

See Send a PDF Letter for a step-by-step walkthrough of the PDF-only workflow.

Multi-page pricing​

The first physical page is included in the base per-piece price. Each additional physical page adds $0.20 per piece. A physical page is one sheet of paper - a page printed front/back counts as one physical page, not two.

Example: a 4-page PDF where each page is a separate side (2 sheets, printed front/back) = base price + $0.20 × 1 additional physical page.

Tips & best practices​

  • Use a clean, professional letterhead for windowed letters - the window creates an impression of official correspondence.
  • For nonprofit appeals, a personalized opening line with %FIRST_NAME% and a handwritten-style signature can meaningfully increase response rates.
  • For PDF newsletters, design at 8.5×11 with 0.5-inch margins to avoid content being trimmed.

Limits & gotchas​

  • Both send modes (cover page and PDF-only) are available for windowed and windowless letters.
  • Additional pages cost $0.20 per additional physical page. A sheet printed front/back is one physical page.
  • Including additional inserts (such as business cards or other physical items) inside the envelope is not supported at this time.