Support yahoo email acct disappears & cannot set up again

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http://androidforums.com – Hi, I got the S3 Friday (liked it better than i5, after 3 i's) & set up my emails including yahoo. The yahoo was working & today I saw a notification of email receipt and swiped it away from the notifications (without reading that yahoo email). Later on I went to look at yahoo mail but the account is no longer shown in the email app account list. I tried to set up the yahoo account again, however the email app complains that the account has already been set up. [Coincidentally, I also updated the phone's sim card today after having the phone number ported over, but I'd not expect (General)