Emailing images can be problematic, as you're now experiencing. The problem is that a lot of email providers will limit the total amount of data that can be attached to an email. In other words, if your ISP limits you to, say, 10MB of attached data and you've got five 9MB files, you'll have to send them one at a time. Or, you'll have to open the original file and save them as a JPEG with a higher level of compression. Or you could also just lower the resolution of the file from, say, 18MP to only 2.1MP.
You don't mention the purpose of the file(s). Are they to be used simply for viewing on a monitor or a smartphone? If so, then you only need 2.1MP for full-HD resolution. Why send someone a 24MP file if they're aren't going to print it out? If the image is going to be used for prints, then you'll need to send a file with the appropriate resolution.
So if sending them one at a time doesn't work, for whatever reason, you could simply create a dropbox or google drive account. Then upload the full-resolution images to the cloud and send the person a link to that drive which will allow them to download the images regardless of their size.