If you are sending photo’s using Outlook 2016 and your images are quite large you can reduce the size of the images automatically before hitting the send button.
Attach your images in Outlook 2016 using the Attach File Option in the Ribbon
Click on the File Menu (from within the message itself)
Under the Info tab you will see the option to Resize large images when I send this message
Click on the arrow up the top left and return to the message, click on Send
Note: Please be aware that the option to resize images doesn’t appear above if you “Insert” “Pictures” directly in to the message. It only works when you attach the images to the message.