I am afraid I have not used Mountain Lion for a long time, PinkSlip, having upgraded my operating system and now using High Sierra. Actually I still have Mountain Lion on a 'guest machine' in Parallels Desktop, but I do not need to invoke it in order to answer your question, for my remark about clicking 'A' applies equally to my present system.
I attach two screen-shots of the top of an email, ready to be written. Each of them shows 'A' in the fourth box near the top on the right. The first is of a situation where several functions are not shown, including Indent/Outdent. The second shows what has happened after I clicked 'A'; Indent/Outdent has appeared.
I hope this will solve your problem.

