can't send email to external party

[LS]

I can't send email to external party but manage to send and receive mails
from my colleagues. Undelivered report stated "Your message did not reach
some or all of the intended recipients"

But I can receive mails from external party.

 

[Brian Tillman [MVP - Outlook]]

I can't send email to external party but manage to send and receive mails
from my colleagues. Undelivered report stated "Your message did not reach
some or all of the intended recipients"

Is that the complete, unedited text of the error message?

 

[LS]

the complete error message are :-

Your message did not reach some or all of the intended recipients

Subject : xxx
Sent : Date & Time

The following recipient(s) could not be reached.