Error sending some email

Well, some smtp servers will only accept email from a valid "internet" domain name, and the return address given is checked out. In some enterprise situations, users send alot of email inhouse, so the return address always checks out. In the users' email client, make sure that the "email address" specified is contactable on the internet, and any other address, (user and/or corp. specific), can go into the "reply to" box ...

Another thing that blocks sending is some servers will not send to an address if it detects that automatic forwarding is setup to send back into the originating network ... That might cause loops in the system as the sender and the recipient will look like the same server and the same user ...

Hope this helps ...

What sort of mail setup do you have? Some post offices, including MS-mail, have a problem with BCC messages. Ask the users if they are sending messages with a BCC, or replying to messages that were sent with a BCC. Replying will generate the message because although the PO is aware of the other addressees, it can't send to them.

Hope this helps.

I do not beleive this is on the client side. I had problems with the Exchane Server for several weeks and I corrected that problem.
I beleive that I created the situation that I am in by changing something within Exchange Server. It worked fine a week ago.
I can resolve all Domain Names at the command prompt by any PC in the building but it seems that the Exchange Server can not.

Does this error happen to the same sites on a regular basis. If so, it very well could be those sites. I had this problem before and found out that in fact the other site either had a problem or their ISP was down. I would call them and see if they are having problems, then check and see if you could send just an email without any attachments.

Good Luck

I am reposting my problem. I found out why this is happening and some of you may be surprised.

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