@Mike – is it a problem on the recipient's side?
Or do you automatically "shrink" your JPEG files when sending per Mail? Could be a preference in your mail app.
Compare the byte count of your original file with the file the recipient can open and save.
Also: did you try to zip the JPEGs before sending? That would retain resolution, too.
Do you have Acrobat Pro installed?
You could transform one JPEG file into a one page PDF; or a bunch of them into a multi-page PDF and control (to an extend) how the PDF is visible in Adobe Reader or Acrobat Pro. To less an extend maybe, if the recipient is using a different PDF reader.
In Acrobat 9 Pro (also in X and avove) you could simply open a JPEG and save the resulting PDF.
In "Document Properties/Initial View" you could customize magnification and other properties.
Also go to "File/Create PDF"; there are various options.
And – maybe the best – in Acrobat Pro see:
"File/Combine/Merge Files into a single PDF".
You could also drop JPEGs in and combine a bunch of them to a multi page PDF.