@Webster's answer is pretty spot on. A reduction of more than 400% may make the file okay to use.
In Illustrator, Check the
Resolution reading in the
Docuemnt Info Panel once you scale down. (
Window > Document Info, then use the panel menu to choose
Linked Images with the image selected)
That will give you an Effective PPI reading based upon scaling. Which may be fine.
A few tips for finding logo when you have been given garbage.
- Check the company's web site. They may have larger raster versions of their logo in use there.
- Check the Company's web site for PDF downloads. You can often cannibalize a PDF and extract a vector version of their logo from a PDF download they offer.
- Check logo sites such as BrandsOfTheWorld.com -- provided the company is large enough, their logo (in vector form) may be available there.
- Last resort - kick back to the company asking for a better quality version. If they don't have a vector format often asking for the "largest file they have" can work. Often these types of things are sent by sales or managerial staff that have no clue about technical requirements. So, they send you the file they use when posting to Facebook or something. Kicking it back to them may force them to actually ask the design staff for an image.
In general a 72ppi image in a commercially printed piece is going to look horrible if the print production people even allow it to go through.