How to fix Apple mail not showing new messages in inbox?

Tap "Mailboxes" to go back and then select "edit" There are several other options there you might double check. Including turning on/off the Unread only mailbox. You can then click "done" and then select which mailbox you want to view .. "all messages" will have all of them in it.

This is just a bug by Apple and has several quick fixes:
Move all items from inbox to a different folder. The most commonly successful fix for this issue is to move all items from the inbox into a temporary folder created on the server. It appears that problematic messages in the inbox can cause the error message.
Upgrade Exchange Server.You may need to apply a service pack to the Exchange server to which your iPhone is connecting. Some users have reported that they need to install Exchange Server 2003 Service Pack 2 to eliminate this error.

This is just a bug by Apple and has several quick fixes:
Move all items from inbox to a different folder.The most commonly successful fix for this issue is to move all items from the inbox into a temporary folder created on the server. It appears that problematic messages in the inbox can cause the error message.
Upgrade Exchange Server.You may need to apply a service pack to the Exchange server to which your iPhone is connecting. Some users have reported that they need to install Exchange Server 2003 Service Pack 2 to eliminate this error.

Few options:

-Delete your "temporary internet files, cookies, cache, history" of the mail + computer/laptop.

-Log out from mail inbox completely and restart the computer/laptop and relaunch the mail account.

-If still experiencing problem, then it could be a server problem from apple. Give it some time.

-At last, contact apple care [if you have the service] or technical support

Please make sure that you are able to see the number of mails that you have selected in your default view. If that is the case, please click on the next page to view your remaining messages. In case you are still not able to see all the new messages, delete cookies and temporary internet files from the browser.

have you signed off then back on?
That may fix it.

Open the inbox and click View All Messages, click unread messages, if you have any on the last page as late arrivals or in folders they will show. This has been happening to all of us while yahoo has been upgrading the classic mail. Yahoo says this is a glitch and will clear on it's own. Did for all of us. Refreshing the page, restarting the comp and clicking on the number don't work. Only Yahoo and time. When it happened to me, my mail alerts also quit working so I had to continually look to see if I had new mail. It was maddening, then all of a sudden one day it cleared and my alerts were restored all on it's own.

This is a very common problem. Upgrading you iphone firmware if it's not current may solve this problem. Or try changing your address for the account from [email protected]" to your yahoo id without the "@yahoo.com"

Otherwise the built-in yahoo option for iphone can be buggy:

1. Delete the Yahoo account on your iphone
2. Create anew account via Other option
3. Fill in the usual user id and password fields
   
4. Under IMAP tab set Host Name under Incoming Mail Server to imap.apple.mail.yahoo.com
5. Under Outgoing Mail Server, in Host Name field set it to cwmx.com

If you have a very large yahoo inbox, you may have to do the following:

1. Go to your yahoo account in a regular browser on your computer. Makesure you're using the new version of Yahoo mail (the one that looks andfeels like outlook).

2. Create a new folder. I called mine "archive - inbox".

3. Select ALL emails in your inbox so that your inbox folder will becompletely empty once you move them (there's a box you can check whichwill select everything). I had over 5,000 emails in my inbox, so thiswould have taken ages using the Classic version of Yahoo mail.

4. Move all emails to your newly created archive folder. Go back intothe archive folder and select any unread/new emails and move them backto your inbox.

5. Go into Yahoo on your iphone and refresh the mail. This will clearout the old emails and download the most recent emails from your inbox.

More info here: http://discussions.apple.com/thread.jspa?messageID=7926883

I have deleted all my mails in all folders...but yet there is still 1 unread message..there is nothing left in my folders inbox, spam, drafts, sent

set GMail to not archive or delete mail after it is downloaded.