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What maker and model is your printer? (Primarily I need to know, in order to tell whether it's a laser-type printer, or an inkjet type... or perhaps another type also.)
Such edge-marks are usually owing to either leaking ink from a cartridge, and/or wrongly positioned or excessively damp paper stock. Check interior for leaked toner/ink, first of all.
Let me know more, and I will advise you further. Thanks.
How recently did you put in new toner?
And, was the cartridge 'Lexmark compatible', and/or refilled, remanufactured, etc.?
Are the toner marks at all textured, grooved, etc.? or are they just plain there, without texturing or variation?
In other words: is the abnormal toner marking on the edge of printouts, looking like anything, or just a featureless uniform stripe?
And is it on every page, period? on the entire edge too, or just some of it?
That sounds as if it might be a marginally (literally, on the margin as well as not-too-severely) damaged 'drum' or developer.
If your toner cartridge includes the shiny, greenish-bluish metallic 'drum', then the cartridge would need replacing for that.
The 'drum' part is very easily damaged by all sorts of things, esp. prolonged direct lighting and touch and moisture and abrasion with almost anything. So be careful with any replacement, not to touch nor moisten etc. the new cartridge's metallic-looking colored 'drum' part.