Without using a plug in FileMaker only sends images as an attachment. If a recipient saw the image inside the body of their email, that was a nice feature of their email program.
The number of emails you can send in one go depend on your email server's settings. You may need to consult with them to determine the limits as many of them have anti-spam settings specifically set up to limit how many addresses you can send to.
There are a number of email plug ins you may want to investigate to see if one will offer the features you want.
Thank you very much! And so speedy too...