Server error: '550 5.5.0 <> invalid address

[MyStarCollectorCar]

I send out about a few hundred group emails at a time and most of them (not all) come back with this message Server error: '550 5.5.0 <> invalid address. They are broken down into 5 groups of 50 or less and I get this message  Server error: '550 5.5.0 <email address here> invalid address. Any thoughts?

[WestCoasterBC]

You should be using a site like mailchimp if you're sending out mass emails, to prevent any blocking that often happens from mass emails be sent. (Seen as spam often blocked)

[MyStarCollectorCar]

Thanks-I've set up for Mail Chimp but this is something that cropped up after I went to Outlook 2010. Is the any correlation?  

[NFtoBC]

Is it possible that some of the addresses are incorrectly entered in Outlook?  There are LOTS of entries returned from a web search on your error message, many related to Outlook.

I second @WestCoasterBC comment about Mail Chimp. It protects both you, and Telus from being punished for sending spam volumes of email.