Q: Can't email picture from new photo app in El Capitan?

The option to email photos should appear in the Share menu, provided you have set Apple's Mail.apps the primary mail reader.

Try the fix in this support document:  See the link below:

     If Share options or Markup is missing after upgrading to OS X Yosemite or El Capitan - Apple Support

Open the link and copy and paste  the Terminal command exactly as it is into the Terminal window, don't try to type it yourself.

It is a harmless command, but spelling errors in the Terminal can be dangerous.

This command does the following: It will reset the launch services database, so the installed applications and the services, document types, etc. supported by the applications can be found.

Paths are searched for applications to register with the Launch Service database.

Valid domains are "system", "local", "network" and "user". Domains can also be specified using only the first letter.

  -kill     Reset the Launch Services database before doing anything else

  -seed     If database isn't seeded, scan default locations for applications and libraries to register

Re: Have MacBookPro late 2013 - upgraded to ElCapitan and Photo.  Now I can not send photos to those on my contact list in Mail.  Worked fine with iPhotos and Yosemite.  What is wrong? What must I do to be able to use Mail to send pictures?

You're welcome, rlmslo 

This also worked for me and I was able to share photos via Mail. However, after restart I am back to missing the Mail option in the share menu.

Should I have to go to terminal each time I want to do this? or is there a more permanent correction?

Thanks for your reply.

Several users reported that the fix has to be repeated after each restart.

This looks like there is a permissions problem with the system library.

I'd try to boot the mac into the recovery partition and to repair the permissions on the  system drive.  See:  https://support.apple.com/en-us/HT201314