Hi all, 
In our company we use Exchange Server 2010 SP1 with 4 servers (2 of them CAS Array with HUB role and 2 of them Mailbox DAG).  There is a problem as with a mailbox account: 

User want to send a mail to approximately 450 recipients as BCC from OWA, but he recieves "You need to choose a recipient before this message can be sent" and "an error has occurred and your request could not be completed. Problem persists, this HTTP contact your help desk with status code: 500 "errors. 

The error report contains 

Exception 
Exception type: System.Web.HttpException 
Exception message: Request timed out.  

If the user sends a mail to one recipient in OWA, it is sent with no problem.

If the user sends the same mail to same recipients in Outlook 2010, it is sent with no problem.

I applied the last Windows Updates, I moved the mailbox to different mailbox database, I rebooted the CAS&HUB servers but nothing changed.

Any help would be greatly appreciated.

Thanks.

• Edited by Ceren Aslanalp Wednesday, August 27, 2014 6:26 AM

Hi Ceren Aslanalp,

For the first error information:"You need to choose a recipient before this message can be sent"

This may be due to: OWA requires you to put semi-colons between the addresses of recipients, not commas as many other email clients allow.

So,please check if enter the addresses in the to/cc/bcc line with semi-colons between them as follows:

User1@yourdoamin.com ; User2@yourdomain.com ; User3..

For the second error information:"an error has occurred and your request could not be completed. Problem persists, this HTTP contact your help desk with status code: 500"

I recommend you try the following method and check if any helps: 

Set-owavirtualdirectory -identity "owa (Default Web Site)" -IRMEnabled $false

Here is a similar thread for you reference:

http://social.technet.microsoft.com/Forums/exchange/en-US/5017098c-0f2a-4749-96cf-385a8ce09137/exchange-2010-owa-error-500-when-retrieving-message-information-or-creation-a-new?forum=exchange2010

In addition, more details about IRM refer to the following article:

Enable or Disable Information Rights Management on Client Access Servers

Best regards,

Niko