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Use a black or dark blue pen: dark ink on a light envelope gives sorting machines the contrast they need. Skip red, green, and light blue ink, which scanners can miss entirely, and skip gel pens on glossy envelopes, which smear. Print in block capitals rather than cursive, and keep the address block away from patterns and edges.
| Ink choice | Verdict | Why |
|---|---|---|
| Black ballpoint | Best choice | Highest contrast on white envelopes; dries fast; exactly what OCR equipment expects |
| Dark blue ballpoint | Fine | Dark enough for reliable machine reading on light envelopes |
| Red or orange ink | Avoid | Some scanners read in red light, which makes red ink nearly invisible to the machine |
| Green or light blue ink | Avoid | Too little contrast against white paper for reliable automated reading |
| Gel or felt-tip pen | Only on matte paper | Wets ink sits on the surface and smears, especially on glossy or coated envelopes |
| Pencil | Avoid | Low contrast and it smudges through high-speed sorting equipment |
Most mail never gets read by a human. Automated sorters photograph each envelope and run the image through optical character recognition. Those cameras and the software behind them are tuned for the highest possible contrast: dark marks on a light background. Black ink on a white envelope is the ideal case. Red ink is the interesting failure: some sorting equipment illuminates envelopes with reddish light, and under that light red ink reflects back almost the same as the white paper, so the address can vanish from the machine's view entirely. The letter then drops out to manual processing, which is slower and more error-prone. A human can read red ink on white paper perfectly well; the machine often cannot.
On plain matte envelopes, almost any ballpoint works. The pen type becomes the problem on glossy or coated envelopes, where gel and felt-tip ink beads up and smears instead of soaking in. One smudge across the postal code and the machine reads it wrong. This is also why printing the address on a label and sticking it on a glossy envelope is often safer than handwriting: laser-printed toner bonds to the surface where wet ink just slides. And for the record, handwriting the address is always a fallback: typed or printed addresses read most reliably, block capitals second, cursive last.
Ink is only part of the readability equation. Sorting equipment also looks for a clear zone: the address block should sit on plain background, away from patterns, logos, and the envelope's edges. Busy envelope designs with artwork behind the address are a genuine cause of mis-sorts, which is why post offices quietly prefer boring white envelopes. Keep the lines parallel to the bottom edge, leave space around the block, and don't let the address crowd the stamp corner. If you're addressing wedding invitations or anything decorative, put the address on a plain label over the pattern rather than writing on the artwork.
Not at all: LetterAgent prints your letter and addresses the envelope for you, so no pen is involved. Recipient addresses show through the double-window envelope exactly as approved, and the sender address shows through the other window as the return address. This guide is for envelopes you address by hand yourself.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is printed and mailed.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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