Why can't I send email through Exchange 2007's SMTP server from an iPhone to external domain email addresses, only internal domain email addresses?

(By the way, SERVER, SERVERNAME, companydomain.com have all been used instead of the actual server and domain name, for security reasons).

This small company of 20 users or so is running an Exchange 2007 server behind a firewall. Exchange server is on the domain controller, and no other Exchange or DC servers are present. Ports 25 (SMTP), 110 (POP3), 995 (POP3SSL) are all forwarded to the static 192.168.0.10 IP address of the Exchange server. DNS records are correctly set up, including an MX record (mail.companydomain.com).

I also forwarded port 25525 (instead of 25, for security purposes) in the firewall (Watchguard Firebox) to the Exchange server, and created a new Receive Connector called OutsideIPHONE which receives mail from 0.0.0.0-to-255.255.255.255 and uses the local IP address 192.168.0.10 to receive email, uses TLS/Basic/Exchange/Integrated_Windows_authentication, and permissions are set for Anonymous_users/Exchange_users/Exchange_servers/Legacy_Exchange_Servers.

I then set up a POP/SMTP email account on one of the user's iPhones. I used mail.internaldomain.com for both POP and SMTP server. I turned off SSL on both (I tried SSL, as I have the ports correctly forwarded, but it did not work -- I'd rather just get it working and worry about SSL later). I used the user's Exchange/domain username and password for POP/incoming authentication, and nothing for outgoing SMTP authentication. It downloads emails via POP just fine. The iPhone can also send an email to any user on the domain just fine. However when I try to send an email from the iPhone to an external email address, such as a GMail or Hotmail account, the iPhone displays the status "Sending 1 of 1" and a progress bar, then after about 30 seconds it times out, with no error message, and reads "1 Unsent Message." And the message sits in the Outbox. The emails the iPhone sends to internal addresses (@companyname.com) immediately send and get moved to the Sent folder.

In Outlook, connected to the Exchange server, every single user can send and receive emails to and from any and all email addresses just fine.

In Exchange 2007 under Organization Configuration, I have a Send Connector called "outbound" enabled. Its FQDN is mail.companyname.com. Address Space tab is set to Domain: *.companyname.com and Type: smtp. In the Network tab, "Use domain name system (DNS) "MX" records to route mail automatically" is chosen and "Enable Domain Security (Mutual Auth TLS)" is checked [could that be the problem?]. "Use the External DNS Lookup settings on the transport server" is not checked.
Source Server is set to SERVERNAME, Site is Default-First-Site-Name, Role is "Mailbox, Client Access, Hub Transport."


Under Server Configuration - Hub Transport, there are 3 Receive Connectors: "Client SERVERNAME", "outside", and "outsideIPHONE" (described above).

I have a feeling Client SERVERNAME is for Outlook connectivity, though I don't know too much about Exchange 2007. It's FQDN is SERVERNAME.companydomain.com. Local IP addresses is (All Available) on Port 587. Remote IP addresses is 0.0.0.0-255.255.255.255. Authentication checked: TLS, Basic Auth (only after starting TLS), and nothing else. Permission Groups checked: Exchange users, Exchange servers, Legacy Exchange Servers (and nothing else).

When I telnet into the server, either on port 25 or 25525 (and if I get 25 working I will probably tighten down port 25 to disallow anonymous access), I can issue a HELO command, and a MAIL FROM command (sender OK), but when I enter an email address (using RCPT TO:) on any domain besides the domain the Exchange server is on, I get:

550 5.7.1 Unable to relay

(And if I type in RCPT TO:user@companydomain.com it works just fine and prompts for DATA). How do I enable relaying for anonymous users through SMTP, using a specific Receive Connector and Send Connector?

Thanks for your help and time,
~Tony


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