What is the email addresses limit to send in one email in outlook in exchange 2013?

To my knowledge Outlook itself doesn’t hold a limit for the amount of addresses that you can send to within a single email. ISPs or corporate mail administrators usually have one of the following limits set or a combination of them:
- amount of recipients for a single email
- amount of emails that you can send in an hour
- amount of emails that you can send in a day

These limits are set to protect their mail server from excessive use or even abuse by spammers. You’ll have to contact your ISP or corporate mail administrator to find out which exact email policies they have in place.

The default limit is 500 recipients, but you can change that value as needed.

http://technet.microsoft.com/library/exchange-online-limits.aspx

Nick is right. 500 is your default.

How do I  test it if the IT Department didn't limit it?

I don't know if there's an easy test.  I'd just ask them.

They said they did nt limit it, but I am getting this message :

Requested rejected your message to the following email addresses:
info@knpc.com
Requested gave this error:
Denied by policy
A problem occurred while delivering this message to this email address. Try sending this message again. If the problem continues, please contact your helpdesk.





Diagnostic information for administrators:
Generating server: asgmail.ALSAYERGROUP.COM
info@knpc.com
Requested
Remote Server returned '550 Denied by policy'

If they limit it .What message I should get?

There is some policy that is blocking that email.  It may be due to its contents, the addresses you are sending it to, or one of a number of configurable policies.

The easiest solution is to have IT go through the logs to get more detail about why that particular email is being blocked.

You'll get exactly the same message.  But the problem is there are a thousand different reasons that you get a "550 denied by policy" error.  You need to isolate which policy is blocking the email.

I send hundreds if emails, only this email got this error, does this means that there is no limit on the sending

Thanks David