There is no stock option to do this.
Here's what I do, and it works pretty good, but isn't perfect.
- Download Reduce Photo Size from the Play storeReduce Photo Size from the Play store.
- When composing an email, click Add Attachment.
- A choice of locations will pop up. Choose Reduce Photo Size.
- Then choose either Select Image or Take a Photo.
- If you click Select Image, then choose Gallery.
- Once you have selected the photo you want to send, click Reduce.
- Now a confusing window will pop up and this is where it gets a little tricky. You really have to know picture sizes as measured in pixels. Click Custom. The smallest photo size will be shown as a default (320x240 or something). I usually use 640x480 for a small 25kb pic, but you could resize up to anything you want.
- Hit OK and then choose the three dots for the menu and choose Done.
That's it!