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73 Outbound SMTP: MercuryC and MercuryE
Choosing between MercuryC and MercuryE

Outbound SMTP: MercuryC and MercuryE

Choosing between MercuryC and MercuryE

Mercury includes two different SMTP client modules – modules that send mail from your sys-
tem to the outside world. The first of these, MercuryC, is called a Relay Client – it depends
on being able to contact one single system and asking that system to send mail on its behalf:
the second, MercuryE, is a full SMTP delivery client, capable of name resolution, and of con-
necting directly to the recipient's mail system and delivering mail. There are pros and cons
for each module – you will need to choose which one most closely fits your needs.

If your Mercury workstation is behind a firewall, or you use a dialup connection to the Inter-
net, then you will typically use MercuryC. MercuryC is ideal for use behind firewalls because
it allows you to channel all your outgoing mail through your approved firewall mail server,
and on dialup links, it will typically keep your connections to the shortest possible times. On
the "con" side, if the host MercuryC uses is unavailable, no mail will be sent from your sys-
tem, and that host must also typically be configured to accept relaying requests from your
server.

If you are permanently connected to the Internet, or if you use a high-speed, rapid connection
link such as ISDN or ADSL, then MercuryE is probably the module of choice for you. Mer-
curyE does not require assistance in delivering mail, which gives you a higher degree of au-
tonomy. MercuryE is also fast, and very efficient. On the "con" side, MercuryE generates a
lot of traffic, both in Name Server requests and in connection requests to the end systems, and
it is not well-suited for use on dialup connections, because in exceptional cases it can take a
long time to time out when delivering to very remote systems.

Configuring the MercuryC SMTP Client Module

MercuryC is the protocol module that is responsible for sending mail from the local system
to the outside world using the Internet SMTP protocol. If it is installed and running on your
Mercury system, you can configure it by selecting its entry from the Configuration menu. In
the descriptions that follow, the word in brackets after the name of the configuration option
is the keyword in the [MercuryC] section of MERCURY.INI that is equivalent to that option.
Smart host (host) The name of the system MercuryC should contact to send mail. MercuryC
is what is known as a relay mailer – it does not attempt deliver directly to the recipient’s mail
system; instead, it asks a larger system to do the delivery on its behalf. You should enter in
this field the IP address or the hostname of the system MercuryC should contact to perform
this relaying. The machine you enter should be running a full SMTP implementation, such as
sendmail or PMDF – at sites with firewalls, the firewall system is usually a good choice.

Connection port/type This is the port on the smart host to which MercuryC should connect.
The standard port defined for this is 25, but in some cases (most notably if you are behind a
firewall) you may have to enter a different port number here. Consult your ISP or Network
administrator to find out if you need to alter the setting of this field. The "type" control allows
you to enable the use of secure (encrypted) data transfers using an Internet standard called
SSL. The default setting, Normal (no SSL encryption) tells MercuryC not to use SSL even if
the smart host indicates that it is available. The second option, SSL encryption via STARTTLS
command tells MercuryC to connect normally, but if the host indicates that SSL services are
available, to issue the command that switches into secure mode. The last option, SSL encryp-