You could use actions to do this. Take one sample image (preferably a copy in case anything goes wrong) and open it. Open the Actions palette (Window > Actions) and create a new action using the "Create new action" button at the bottom of the palette. Give it a name, such as "Resize for Email", or whatever makes sense to you. When you click ok, the red "record" button lights up in the actions palette.
Go to Image > Image Size and make sure "Resample Image" and "Constrain Proportions" is checked. Change the rest of the settings to something appropriate, for example, change the resolution to 72dpi, or change the Width or Height to a suitable size. Click ok, then press the "Stop" button in the actions palette. Close the image (no need to save it).
That's the hard work done. You can now reuse that action in future without having to go through the above. Put all the photos you need resized into one folder, go to "File > Automate > Batch". Your action should be selected by default, but if it's not, have a look in the "Action" drop down list and select it. For Source, choose Folder, and navigate to your folder. For Destination, choose Save and Close. I would also suggest checking "Suppress Color Profile Warnings". Click Ok, and it will resize the whole folder for you.
Keep an eye on it for a few images; it might need you to keep pressing "ok" if there is a query about the file saving options. Also, this will overwrite the original images so make sure you make a copy of your images before you run the batch.