If you're taking a photograph with a camera is very likely that the photograph will be of quite a high resolution.
When you're dealing with attachments to emails the first thing you ought to think about is to what used there will be put. If they just to be read online the resolution can be as little as 96 DPI, if they have to be printed by the recipient you should aim for a resolution of 250 DPI. If there just in black and white resolution should be at least 300 DPI.
If you make sure that these resolutions are stuck to you shouldn't have very much problem with sending by email. There is a free photographic application called gimp that you can use to adjust these.
Please get in touch if you would like any further help.