domain name system - Exchange 2010 OWA send connector issue

I have problems sending emails outside organization using OWA (Exchange 2010 installed on SBS 2010, domain is domain.local, local DNS). Web-server and email server are hosted remotely, I am using pop connector to grab emails to Exchange 2010.

I have created two send connector, one that handles internal emails and one for external email. The problem is connector for emails over internet, which is configured like:

Addres Space SMTP, *, 1

Network Route email throught the following route host Smart host
authentication: Basic authentication over TLS + username, password

If I don't use smart host I get the following error 451 4.4.0 Primary target IP address responded with: “454 4.7.5 Certificate validation failure.”

If I use smart host when using OWA outside of organization (different ISP), message gets stucked in a queue without being sent.

What am I doing wrong when configuring send connector?

Answer

You likely only need one send connecter, and since your primary mail server is remote, I assume you want to send email through it (aka smarthost). That way you don't need to worry about DNS A records, MX, PTR, SPF, and all the other mail configuration stuff. Just set your send connector smarthost to your mail provider's SMTP server and ensure you are authenticating so you'll be allowed to relay. If you don't authenticate, they'll almost surely deny your email (which is likely why it's sitting in queue) because that would be a "open relay", which is a bad thing.