I am a business user of yahoo. In other words I pay for my own domain. In the last week I have been getting no push notification of inbox activity and I can't download the messages that are there. I have reverted to windows where I have no problem. Does any one know what has gone wrong. BTW I get the same problem on IOS5 and6

Go into Settings > Mail, Contacts, Calendars and make sure Fetch New Data is set to Push. Open the setting by tapping on the arrow to the right, go into the Advanced, and make sure that Yahoo is set to Push as well.

If that's not the problem:

Go to Settings > Mail, Contacts, Calendars > Yahoo account. Turn off Mail, open the Mail app to make sure it clears, then go back and turn it on again.

If that does not work, try the same thing, only delete and re-add the account instead of turning Mail on/off.

This clears up most issues.

Thank you for the reply. I followed your suggestions and waiting to see the result when someone sends to me

You can always send something to yourself. I do all the time, for testing. Though it does work best if you have more than one email account.