550 5.1.1 <xxx@xx> is not a valid email mailbox ???? Help!

[Milly Staples [MVP - Outlook]]

Learn how to post a question:

See that large white space beneath the subject line? Use it to provide at least a modicum of information about what you are trying to accomplish. Otherwise, you are wasting our time and yours when someone has to come along and try to pry information out of you.

 

[Lisa P]

Thanks for your kind explanation, Milly.

I've been attempting to resolve an issue with Outlook all day today. I was
corresponding earlier (12 hours earlier!0 with someone who gave me a couple
of suggestions, which I tried. When I came back to see if any more info was
available to me, I accidently submitted my blank question.

Perhaps you can help. I can send an email to everyone in my address book
EXCEPT those that have yahoo addresses. I've contacted my system admin, as
well as my ISP. I'm wondering if it my be my security settings, although I
can't understand why this all of a sudden happened.

I use Microsoft Outlook 2003, Version 5.1.2600 Service Pack 2 Build 2600

Any suggestions would certainly be appreciated.

Lisa P