Symptoms
- Diagnostics report: No external IP addresses detected. Domain XXXXXXXXXXX must specify a HELO/EHLO domain, otherwise some email servers will not accept emails from this domain.
- When sending a message the remote mailserver gives an error response to the HELO or EHLO command.
- Some domains will not accept mail from me it either stays in the Outgoing queue or is returned as undeliverable.
Cause
When Softalk Mail Server connects to another mail server to send a message by SMTP, it needs to identify itself. The SMTP standard requires that the server use its Fully Qualified Domain Name (FQDN), or, if the FQDN is not known to the server, it may use an Address Literal. This is its IP Address in square brackets e.g. [83.104.94.162].
Resolution
The Fully Qualified Domain Name or Address Literal should be entered into the Softalk Mail Server Administrator so that Softalk Mail Server knows how to correctly identify itself when issuing the EHLO/HELO command.
This can be entered once for all domains configured in Softalk Mail Server by going to Settings, selecting the Sending tab, checking the box "Specify the default EHLO/HELO domain/IP address" and then entering the appropriate value in the text box below.
The default value can also be overridden on a per-domain basis by going to the Sending tab in the Domain Properties dialogue box and selecting "Specify the EHLO/HELO domain/IP address" option and entering the appropriate value there.
More Info
RFC 2821 – 4.1.1.1 Extended HELLO (EHLO) or HELLO (HELO)
RFC 2821 – 4.1.3 Address Literals
Detail
If Softalk Mail Server is running on a computer that is directly connected to the internet (where one of the interfaces has a Public IP address) then Softalk Mail Server will detect this. It will attempt to perform a reverse DNS lookup to find the Host Name for this address and, if found, will use this value. Note that users with this configuration will not see the above error message from the Softalk Mail Server Diagnostics.
If the computer running Softalk Mail Server is not directly connected to the Internet then it is most likely that there is a NAT (Network Address Translation) system that maps internal addresses to external addresses. In this case the mail server should use the IP address of the public interface of the router. You can identify your public IP address from the router configuration or, if you have a static IP address, from your ISP. Also, if you visit http://checkip.dyndns.org then this will display your public IP address.
Once you have this Public IP address you should find out what the Fully Qualified Domain Name is for that address. You should be able to do this by performing a reverse DNS lookup on the IP address you have just obtained. The nslookup utility that comes with most versions of Windows will perform a reverse DNS lookup on an IP address. Open a Command window and type "nslookup <address>" where <address> is the IP address. If the reverse DNS lookup is successful there should be a Name: response including the host name. This is the value you would enter into Softalk Mail Server. Alternatively you can try the Reverse DNS lookup at www.dnsstuff.com. If you cannot identify the FQDN, and you have a static IP address, enter the public IP address in square brackets, e.g. [83.104.94.162].
If you are unable to find the FQDN and you have a dynamic IP address, use the internal IP address, entered as an address literal e.g. [192.168.0.1]. Note, this is not fully compliant with the standard and so can result in the mail you are trying to send being rejected.