We are using Server 2012 with Exchange 2013 installed, my boss has an excel list with email addresses that he copies and paste from. All the email addressed on the list are confirmed and work on an individual basis.
He is using Outlook 2013, when he copies multiple over to the To column not even the BCC column but the To section in Outlook he gets the below bounce back for some. It is never the same people that get the bounce back either, it is random with the errors below. So say out of 50 he might get the bounce back 10 times, everytime, but it is always 10 random people.
I read that 500 is the default setting for max recipients in both outlook 2013 and exchange 2013 but can't find where to check that anywhere. Again all addresses are confirmed correct.
Here is a sample, he gets an email with this same bounce back for however many don't through that time.
mail1-5.xxx.com rejected your message to the following email addresses:
mail1-5.xxxxx.com gave this error:
The email address you entered couldn't be found. Please check the recipient's email address and try to resend the message. If the problem continues, please contact your helpdesk.
Diagnostic information for administrators:
Generating server: FT-EXCHANGE.fosterthomas.local
Remote Server returned '550 5.1.1 User Unknown'
I x'd out the name and domain because they are a big client but he can email them indiviudally just fine but when he copies over and the email is confirmed to have copied properly. He gets that bounce back.