Citadel on Raspberry Pi - Connection broken during SMTP conversation

Question

I recently got a Raspberry Pi and decided to make a small E-mail server using the Citadel software. I can receive E-mails from both addresses I am trying to send to, but I can't send to them. The two E-mails are live.com and gmail.com addresses, and I get the following errors after leaving it over night:

Live:

1) Connection failure: Connection broken during SMTP conversation while talking to mx4.hotmail.com;

2) AAAA-lookup mx4.hotmail.com - DNS server returned answer with no data;

Gmail:

1) Connection failure: Connection broken during SMTP conversation while talking to gmail-smtp-in.l.google.com;

2) Connection failure: Connection broken during SMTP conversation while talking to gmail-smtp-in.l.google.com;

3) Connection failure: Connection broken during SMTP conversation while talking to alt1.gmail-smtp-in.l.google.com;

4) Connection failure: Connection broken during SMTP conversation while talking to alt1.gmail-smtp-in.l.google.com;

All of the ports on my firewall (corresponding to the mail server) are open, and I can ping all of the addresses listed above however, they still persist on not sending.

Are there any other things I can try that may fix this problem?

Thanks!

Answer 1

To get more details on why connectivity is failing, use the Telnet utility to debug the connectivity. You can establish a connection to port 25, the well-known port for SMTP connections and then use telnet to issue the commands used by email clients and other SMTP servers to transmit email to an SMTP server. E.g., once a connection is established to an SMTP server, to transmit an email message, you can first say "hello" to the server using an helo or ehlo command. Then issue a mail from: sending_address command, substituting the email address you would be using as the "From" address for sending_address. Then issue a rcpt to: recipient_address command where recipient_address is the email address you would use as a "To" address. You should see "sender ok" and "recipient ok" responses after you enter those commands. Then type the command data and hit enter. You can then type whatever you like for the body of the message. The email addresses you entered previously are not necessarily those that the recipient will see. What the recipient will see as "from" and "to" addresses can be provided by typing From: from_address then on the next line To: to_address where you will provide the "from" and "to" address you want the recipient to see. Normally they would be the same as the email addresses you used previously, but they don't have to be. Then, you could type Subject: your_subject and after that line whatever you wanted to appear in the body of the message. E.g. A test. Then hit Enter and type just a period on the next line. That terminates the message. You can then type quit to disconnect from the email server. I've included what you might see below:

$ telnet mx4.hotmail.com 25
Trying 207.46.8.199...
Connected to mx4.hotmail.com.
Escape character is '^]'.
220 BAY004-MC6F10.hotmail.com Sending unsolicited commercial or bulk e-mail to Microsoft's computer network is prohibited. Other restrictions are found at http://privacy.microsoft.com/en-us/anti-spam.mspx. Fri, 24 Mar 2017 14:26:41 -0700
helo example.com
250 BAY004-MC6F10.hotmail.com (3.22.0.29) Hello [192.168.55.167]
mail from: [e-mail]
550 DY-001 (BAY004-MC6F10) Unfortunately, messages from 192.168.55.167 weren't sent. Please contact your Internet service provider. You can tell them that Hotmail does not relay dynamically-assigned IP ranges. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
Connection closed by foreign host.
$

I used example.com in the helo command above. An email server delivering email to an SMTP server would typically provide its fully qualified domain name (FQDN) name there, but you can use whatever you like, e.g. example.com or the FQDN associated with your system. I also replaced the actual IP address of the system from which I connected to the SMTP server with a private IP address; you would see the public IP address of the system from which you ran the telnet command.

I stated that what appears above may be what you will see, because I suspect the issue may be the one that is in the output from the Microsoft server that handles email for live.com address. I.e., because much spam originates from DHCP-assigned IP addresses, often because home users have systems compromised by malware that attempts to use those systems to distribute spam, most large email service providers have their email servers check lists of address blocks used by Internet Service Providers (ISPs) for dynamically assigned addresses for their customers and automatically reject email from any IP address known to be dynamically assigned.

You have a couple of options, if you wish to use your own email server for sending email, if your server has a dynamically assigned address rather than a static one. You may be able to obtain a static IP address from your ISP; typically, if the ISP will provide such addresses, there will be an additional charge. Or, if you have a home service, you may have to switch to a business service at a higher price. Or you can configure your email server running on the Rasberrry Pi to use a smart host. I.e., you configure your email server to route outgoing email to another SMTP server, which will relay the email to the recipients' email servers.

You could configure your email server software to use the SMTP server designated by your ISP as the smart host or you can use a smart host provided by an email service provider. Some companies that provide mailing list services will allow you to create free accounts for sending email through their email servers for those who only need to send a few thousand email messages per month; hopefully for those companies, those whose needs grow in the future would purchase service from the company. I've used SparkPost, but with Sendmail rather than Citadel, so I can't give you specific instructions for Citadel, if the issue you are encountering is due to your system having a dynamically assigned address.