Attaching photos to emails question

I'm not sure this is the proper place to ask this question; if not, forgive me and redirect.

When I take pictures with my Canon camera I transfer them "as is" to my computer. I have just noticed that some of them are 20 inches by 14 inches and approx. 20Mb at 300 dpi. This seems to me rather extreme.

I am on a trial 5G network and I have a workhorse of a laptop but not all my "receivers" do, so I presume these dimensions, etc. could cause some people problems . So my question is: What is the best size, dpi, etc. to attach pictures to emails? I doubt very much that my receivers print the photos and even if they do they would probably print ordinary 4 x 6s.

Thanks in advance for all advice.

That is impossible to answer it depends on the recipients what they want and there connection and there email server. You can compress them with a jpg compressor you could zip them up. Are these raw or jpg if raw they may not be able to view them.

Thanks a lot for your advice.
I have quite a few friends around the world so it's difficult to say what kind of equipment they have; I know one who is still using XP. I would say that most of them will just look at my pictures on their screen/monitor, while the occasional one or two will print the occasional one or two as regular 4x6s. I just read an old article on a US newspaper that suggests that a jpg of between 2 and 3 Mb should serve all "normal" purposes. I don't know how much to rely on that advice since"normal" is rather subjective.