This is the first time (and I hope only/last) time I am on an Apple Support Forum.
I have some information and would like some help if someone really knows what they are doing.
My first and only Mac has been a MacBook Air. Two years and it has been excellent. I upgraded to Lion, after Snow Leopard. Everything was great. I upgraded to Mountain Lion...and now Yahoo Mail is a disaster in the Apple Mail program. Thinking there was a problem with the install, I did a complete format and fresh install of Mountain Lion and only brought files back on - I started all settings from scratch. After this fresh install, still my sent mail disappeared, it never appeared in the "sent" mail folder. Sometimes when I was sending mail it timed out, too. With settings under Mountain Lion, it brought in all my archive yahoo folders that I didn't want/need access to, so when I went to delete one (not accustomed to IMAP settings, I had only ever used POP with yahoo) and I ended up deleting over 3,000 emails I archived for my own publishing/writing and such. Bye-bye two years of saved correspondence. I contacted Yahoo immediately and was not able to rebuild that folder...
I was pretty angry, but let the issue go. I still was noticing that I had the disappearing "Sent" mail issues, and wanted to just solve that and move on - every system can have issues, right? Well, both times I have spoken to Apple they have told me, "We haven't seen problems like this." Both times. Almost half the events/problems listed in this thread match my exact problems of "timing out", disappearing items that are sent, items that are sent and received by people not appearing in either my Mail "sent" folder nor my Yahoo sent folder on the server. ---Yes, "Keep a copy of sent messages on the server" is checked and has always been)
Then, when I realized that going back to POP using my yahoo account might solve this - going back to the settings when it worked without issue - it seems this is impossible under Mountain Lion. I tried manually entering settings listed from Yahoo for POP. That didn't work, even though it worked for almost ten years with Outlook 2003, Outlook 2007 and Apple Mail under Snow Leopard and Lion. Now, for whatever reason (and I would like to know why) IMAP is now the only option for Yahoo.
After almost an hour and a half of work with me over the phone on the first call three months ago, I finally give up and ask the obvious question: How do I get this set back to POP for this yahoo account? The answer, after some shuffling: "You can't do that anymore. It's not an option." It's not like I misunderstood the answer, or they misunderstood the question, because I repeated it.
So, after two years of slowly adopting an Ipad and the Iphone 5...my main issue is with Mac's Mail program. I never thought I'd own an iphone, ipad and MacBook Air and find my main problem to be with the Mail program. Basic stuff. I never thought I would be longing for the days of Outlook.
The Apple Mail program won't work, nor will it allow me to set it to work in the way that was easiest and seamless three months ago. In some way this would all make sense if things worked better across all three platforms (ipad, iphone and mac), but it doesn't now. Over three hours on the phone, and regardless of what many people have added to this thread, no aknowledgement this is even a problem for Mail.
Aside from opening a webpage, checking email and using a mail program is about as basic as functionality gets in a device today. Like others have said, it generally works like it should on my iOS devices. Sent stuff goes where it should - "sent" folders.
What now makes me angry, after reading all ELEVEN pages of this thread, is that both support calls I made, I asked three - THREE - different support personnel "Is this an issue you're having with Mountain Lion and IMAP?" or "For comfort, I need to know - are you having other issues like this with other customers?" All three answered, "No. First time I have seen this." Looking through all eleven pages of this thread makes it clear this is either willful deception for some reason, or - despite how truly good natured the support personnel at all levels were - astounding incompetence.
I was a late adopter, and for two years I had (past tense) grown to love Apple. I sang their praises because things did what they were supposed to do. I am (no sh#$) now looking at Windows 8 ultrabooks.