Hi I  am vishnu i am using O365 E1 plan and i have cloud space 50GB i have used only 30gb and i start using outlook 2007 so i have configured  through exchange but mail not getting download fully pop up coming mailbox full(mail file that is OST size showing 20 GB after that mail not downloading please help me 

I recommend you ask your e-mail administrator.  If you are the e-mail administrator, then I recommend that you open a support ticket with Office 365.  If you still want to address this in a forum instead of following the correct support channel, I recommend that you post this in the Exchange Online (Office 365) Forum: http://social.technet.microsoft.com/Forums/en-US/onlineservicesexchange/threads

Hi,

In my opinion, the mailbox full nitification is related to the mailbox quota or mailbox folder limits in Office 365:

https://technet.microsoft.com/en-us/library/exchange-online-limits.aspx

Please close Outlook and only use OWA to confirm whether the mailbox full email is received in Inbox folder and if you can send and receive messages normally. If the issue only happens when using Outlook 2007, please try the latest Outlook 2013 to have a try.

If the issue persists, please follow Ed's suggestion to ask a question in Office 365 (Exchange Online) forum for more help.

Regards,