We can receive but cannot send out emails through outlook 2010, we are using yahoo bizmail accounts. Our Isa server 2004 is set to allow unrestricted access. I have tried changing outlook smtp ports from 25, 587 and 465 Ssl to no avail. But configuring the same yahoo account via outlook outside of the office, sending email is fine. The strange thing is users with gmail accounts behind the Isa server in the same office network, using smtp ports 465 or 587, is also working fine.
Telnet smtp.bizmail.yahoo.com 587 does not work but telnet smtp.gmail.com 587 gives 220. But testing both in a different network (at home) gives both 220 results.
What do you think is the problem? I read that it can be Dns issue? How do we check for that?