So far all I've come across are those that have the same issue, but no solution or only temporary fixes. I have one yahoo mail account I use for personal stuff and one I use for my business. I just got a iPhone 4S, left AT&T for Verizon, 16GB, and immediately upgraded to iOS 6, but I've seen a lot of the same complaints with previous versions. I don't care were the problem is, I just want to know where it is and how to fix it. I added both accounts and set the business account as the default account. All mail pushes to the personal account, but not to the business account. Exception-an email from a banking alert or other similar account notifications will push and will also push the other emails that were hung in the pipeline. Email from individual customers won't push. I will occasionally get the "downloading 1 of x" then the account shows "updated" and no emails come through. Looking for answers beyond restarting the phone, deleting and adding the account back. If there is a fix, please post.
I can imagine how important the business email account is for you. We don't want you to lose out on a client because of the trouble. I have thoroughly investigated the trouble and found that Yahoo has recognized the failure is on their end. They're currently working on a permanent fix but have posted a workaround that many customers have advised has worked for them. I know you expressed looking for answers beyond the general options but I do encourage you to review these to see if they may work.
Step 1) Set the mail app to show only the last 50 recent messages by going to Settings > Mail, Contacts, Calendar > Scroll down to Show > change to 50 Recent Messages. Restart phone by holding down the home button and the sleep/wake button at the same time.
Step 2) Delete the Yahoo! Account and then re-add it. Sometimes the settings and server information gets messed up when you restore from a backup.
Step 3) On the web interface for Yahoo! Mail, make a test folder and move the emails into this folder one-by-one. Sometimes there is one email that is causing the push to malfunction and once you find this email, the issue with push Yahoo! mail should be fixed.
Step 4) Go on to your Yahoo! mail with another computer, change your password, then log on and log off with the new password to make sure it works. Go back to your iPhone and change the settings to the new password.
Please keep us posted to whether these worked for you.
Please follow us on Twitter @VZWSupport
All email starting functioning/pushing as it should from both of my yahoo mail accounts two days ago, without changing any settings. Hopefully, it's resolved.