Are you attaching a file or looking at the attachment .
Which email prog outlook?
or a web based one such as hotmail or googlemail?
Sometimes when opeing a file type the computer forgets which programme is associated with jpegs and uses another prog instead. (I'm assuming the file is a jpeg and it has the .jpg extention at the end if this is missing widows can have trouble opening the file)
To check the file association right click the file, choose properties then check second line down says opens with... this should be windows pic and fax viewer if not then change it to this.
NB this This change affects all files that have the same file name extension as the file you selected.
Post back if still having problems.