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Black lines running top to bottom on a fax almost always come from a dirty spot on the scanner glass or a worn feeder roller on the sending machine. A single speck of toner, ink, or correction fluid on the glass reads as a solid black stripe on every page. This is a sending-side problem, not a receiving one.
The lines point at the sender. Fax machines do not "draw" pages the way you might imagine: the sending machine scans the paper, and anything stuck to the scanner glass gets scanned along with the page. Since the spot does not move while the page feeds through, it renders as a continuous vertical line on the transmitted image. If you received faxes from several different senders and they all show lines, suspect your own machine's printer instead: print a test page, and if the lines show up there too, your printer (not any sender) is the culprit. If only one sender's faxes have lines, the dirt is on their glass and no amount of fixing on your end will help.
The thin feeder glass is the one that matters here: many machines have a narrow glass strip dedicated to the document feeder, separate from the large flatbed glass used for copying books. People clean the big glass and miss the strip, so the lines survive.
Unplug the machine first. Lift the feeder cover and find the narrow glass strip; wipe it with a soft, lint-free cloth barely dampened with isopropyl alcohol or glass cleaner, then dry it fully. Clean the white calibration strip opposite the glass too, since grime there can cause light or dark bands. Check the feeder rollers for grooves or flat spots and wipe them down. Then run a plain copy: if the copy is clean, the next fax you send will be clean too. This is the single most common fax-quality fix in existence, and it takes about two minutes.
| Symptom | Likely cause | What to do |
|---|---|---|
| Sharp black line(s), always in the same place | Dirty scanner glass or damaged roller on the sender's machine | Clean the sender's feeder glass and rollers |
| Overall blur or faded text | Low scan resolution, bad line connection, or a failing print head | Raise the resolution setting, resend, or check toner |
| Lines on ALL received faxes plus on copies | Your own machine's print drum or fuser | Clean or replace the drum cartridge |
| One side of the page darker than the other | Uneven lamp or dirty calibration strip | Clean the white strip and glass on both sides |
Not on the sending side. When you fax through an online service, your document is a file: there is no glass, no roller, and no scanner to get dirty, so sender-side lines cannot exist. That is actually a practical fix for a machine that keeps streaking. On the receiving side, a physical machine that prints incoming faxes can still put lines on the printed pages, but then a plain copy will show the same lines, which confirms the printer is at fault. With LetterAgent, you send a fax by describing it to your AI assistant: per-fax quote with the page count verified, you approve the exact total, pay once through Stripe, and the fax is sent, with no scanning hardware in the path at all. LetterAgent covers US and Canadian fax numbers only and cannot receive inbound faxes. Faxing is currently available in testing while activation is in progress, so it is described as available in testing, and a successful send on any given day is never guaranteed.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
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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