If your Citadel server is running, but you cannot send outbound mail, check the queue by logging in to WebCit as an administrator and selecting "Administration" followed by "View the outbound SMTP queue". If you see a lot of messages stuck in the queue with statuses such as "Connection refused" then there is a problem making outbound SMTP connections.
This is a problem with either your host operating system configuration or your Internet connection. You would be experiencing the same problem with any mail server, not just Citadel. Here are some troubleshooting steps you can take.
First, check to make sure your resolver is properly configured. You can't send mail if you can't find the recipient's servers. Go to a shell prompt on your server and try a command like this:
$ nslookup
> set q=mx
> gmail.com
Server: 10.0.0.1
Address: 10.0.0.1#53
Non-authoritative answer:
gmail.com mail exchanger = 50 gsmtp147.google.com.
gmail.com mail exchanger = 50 gsmtp183.google.com.
gmail.com mail exchanger = 5 gmail-smtp-in.l.google.com.
gmail.com mail exchanger = 10 alt1.gmail-smtp-in.l.google.com.
gmail.com mail exchanger = 10 alt2.gmail-smtp-in.l.google.com.
In the above example we are looking for the MX (Mail Exchanger) servers for gmail.com (Google Mail). The above results are correct -- we were told the addresses of five servers that receive mail for that domain. If you do not get these results, your resolver (DNS) is broken and you must fix its configuration before Citadel can send mail.
Assuming that your resolver is good, now you can test to see whether you actually have the ability to reach external mail servers. Try to telnet to one of the servers you just learned about, on port 25. For example:
$ telnet gmail-smtp-in.l.google.com 25 Trying 209.85.133.114... Connected to gmail-smtp-in.l.google.com. Escape character is '^]'. 220 mx.google.com ESMTP b12si3344116ana.1
If you get this far you can type 'QUIT' to end the connection. You are looking for the remote server to answer immediately and display a protocol prompt that begins with a three-digit number starting with the numeral 2.
If you get any other result, you have a problem. For example, you might get a "Connection refused" error, or perhaps the session will simply hang while waiting for a connection. Either your server does not have a proper connection to the Internet, or more likely your ISP is blocking outbound connections on port 25.
Port 25 blocking allows ISP's to block spam sent out through their networks, but it tends to punish the innocent that have a need to send through e-mail servers other than those belonging to their ISP. The ISP's that block port 25 require their SMTP server to be used instead of the remote SMTP server or a SMTP server running on your computer. If this is the case, you have several options: