I am using Outlook 2007. I have always used a backdoor server for my outbound emails. Yesterday, that door was closed so I had to start using the outbound server associated with my domain.

However, I am unable to send emails though this (which is why I didn't use it before).

When I contacted the hosting company they said it was fine on their end and that there was a firewall blocking the emails on my end.

Yesterday, my emails would eventually go out but it may take an hour (and 10-20 send/receives) before it would.

I located the only known firewall on my computer (Windows Security Firewall) and checked the settings. It is set to allow Outlook to send. Just to be sure, I completely disabled it and still tried to send to no avail.

Im not sure it's a firewall because I have always been able to send from Outlook and the server I was using before was using the same port (25 &/or 2525).

Any ideas??

Sorry to bump... but this is still troubling me. Its totally sporadic... I can't figure it out and its driving me crazy...

Have you confirmed your account information is correct in Tools > Account Settings > [Highlight an Account] > Change.. Most servers require login or a connection from the same network the server serves to allow mail to be sent.

When you send and receive, click the 'Send/Receive Status... ' in the status bar and select 'Details', then click the error tab. That should tell you why sending mail is failing.

You might also check the settings in any antivirus software. Many interpose a relaying component to scan outgoing mail between your mail client and the server.

Another potential firewall could be your router...

You can verify packets are getting to the server by opening a command prompt and issuing "telnet your.mail.server.com 25". You should receive something like "220 your.mail.server.com ESTMP" as a response confirming you can connect to the server. Type "quit" to end session.