Connections

Network connections are established to the ISMail SMTP server in order to receive messages ('Incoming' connections), and initiated from the ISMail SMTP server in order to send messages ('Outgoing' connections).

Messages from a remote account to an ISMail account require only an incoming connection (from the remote mail server).

Messages from an ISMail account to an ISMail account require only an incoming connection (from the email client program).

Messages from an ISMail account to a remote account require both an incoming connection to transfer the message from the email client to ISMail, and an outgoing connection to transfer the message from ISMail to the remote mail server, where it is then delivered to the recipient.

Incoming connections can be configured to use certain network ports and IP addresses. The maximum number of incoming connections can also be configured.

Outgoing connections can be directed using the 'Smarthost' option. The maximum number of outgoing connections can also be configured.

In addition, the maximum message size transferred over a connection (incoming or outgoing) is configurable.

SmartHost

Normally, ISMail will send messages directly to the mail server of a recipient. A 'SmartHost', however, can be used to relay all messages to another mail server in order to workaround problems with firewalls, resolve outgoing port restrictions (port blocking), or to insure message delivery to mail servers which place various restrictions on senders (e.g. disallow dynamic IPs, use reverse IP lookups).

Note: Incoming port blocking can be tested using the mail server test utility available on the instantservers.com web site. Outgoing port blocking can be tested by opening a DOS window on the mail server machine, and entering 'telnet instantservers.com 25'. If an SMTP 'welcome' message appears, then port 25 (outgoing) is not blocked (enter 'quit' to exit this connection). If a connection is not established, then port 25 may be blocked. Futher testing should be done to determine the cause of the failed connection.

Adding A SmartHost

To add a SmartHost (using standard port 25):

1. On the 'Connections tab, select the SmartHost checkbox.
2. Enter the name or IP address of the SmartHost.
3. If all messages should only be sent using the SmartHost, select the 'Use SmartHost Exclusively' box. If messages should be sent using the SmartHost only if direct sending fails, deselect the 'Use SmartHost Exclusively' box.
4. If the SmartHost requires authentication, select the 'Authenticate' box and enter an 'Account Name' and 'Password' for an account existing on the SmartHost.
5. Click 'Apply'.

To add a SmartHost (using a non-standard port):

1. On the 'Connections tab, select the SmartHost checkbox.
2. Enter the name or IP address of the SmartHost, followed by a color (':') followed by the port number (e.g. example.com:27 would use host 'example.com' on port 27).
3. If all messages should only be sent using the SmartHost, select the 'Use SmartHost Exclusively' box. If messages should be sent using the SmartHost only if direct sending fails, deselect the 'Use SmartHost Exclusively' box.
4. If the SmartHost requires authentication, select the 'Authenticate' box and enter an 'Account Name' and 'Password' for an account existing on the SmartHost.
5. Click 'Apply'.

Outgoing Connections (min: 1, max: 20, default: 2 connections)

The maximum number of ISMail outgoing connections active at any time may be specified. A value of 1 will force outgoing messages to be sent serially, one at a time. A larger number may be used so that a slow connection (or a large message) does not block other messages from being processedat the same time.

Setting the Maximum Outgoing Connections

1. On the 'Connections tab, under 'Outgoing', enter the maximum number of outgoing connections.
2. Click 'Apply'.

Incoming Connections (ports, IP addresses)

The SMTP server listens on port 25 for incoming connections by default. The SMTP server listens on all available IPs (network interface) for incoming connections by default. However, the listening port may be changed, and the listening address may be set to a specific IP value.

A secondary (alternate) port may also be used to receive SMTP connections. As with the primary port, the secondary listening port may be changed, and the secondary listening address may be set to a specific IP value.

Setting Incoming Ports and IP Addresses

To set the Primary and/or Secondary SMTP port and IP address:

1. Select the 'Connections' tab.
2. For the Primary SMTP server, enter the incoming port number (1-65535)
3. For the Secondary SMTP server, enter the incoming port number (1-65535)
4. Click 'Apply'.

If the primary and secondary ports are the same, and no IP address is entered, then only the primary values will apply.

Caution: certain network ports are already used by ISMail or other programs. If a port in use by is chosen for the ISMail primary or secondary port, then ISMail or the other program may not function correctly. See the mail logs for more information.

Incoming Connections (min: 10/1, max: 100/10, default: 20/5)

The maximum number of ISMail incoming connections active at any time may be specified. The maximum number of ISMail incoming connections from any single host (IP) active at any time may also be specified. If a particular mail server is placing a large load on ISMail, the maximum number of incoming connections from any single host can be set to 1 to reduce this load. A larger number may be used so that a slow connection (or a large message) does not block other messages from being processed at the same time.

Setting the Maximum Incoming Connections:

1. Select the 'Connections' tab.
2. In the 'Incoming' box, enter the maximum number of incoming connections (Total)
3. Enter the maximum number of incoming connections from a single IP (From a Single Host).
4. Click 'Apply'.

Setting the Maximum Message Size

To set the maximum allowable incoming/outgoing message size:

1. Open the 'Connections' tab.
2. Set the 'Maximum Message Size (MB)' field.
3. Click 'Apply'.