The choice depends, first of all, on the availability of a good SMTP server. If your ISP SMTP server is able to handle a lot of messages in a fast sequence or even sending messages simultaneously, using an SMTP server is faster and more reliable, since your SMTP server is “closer” to your computer than the single recipient’s e-mail server.
However, some providers try to prevent users from using the server for spamming purposes by imposing restrictions on the number of messages that can be sent within a specific time span and the number of messages that can be sent simultaneously. For instance, an SMTP server could accept no more than a message every 5 seconds and not allow sending more than 2 messages at a time. All messages that exceed these restrictions will be rejected with an error. This does not mean that the server or the software aren’t working properly, but rather, that it will be necessary to set up in a different way the sending timing option in the Advanced settings section.
In such cases, it could be faster and more convenient to use the direct send. The direct send requires a little more time to deliver each message (since it has to make a request to the DNS server and the e-mail server could be very “far” from the user’s PC), however this time increase is compensated by the possibility to send more messages simultaneously without having to add extra pauses between messages.
Direct send is also useful when a sending operation has to be performed using a connection without knowing the SMTP server (typically the case when using a notebook “away”, meaning not in the office or at home – common in the case of a public access wireless network).
The Advanced settings section allows you to fine-tune the sending timing. This is useful to perform a sending operation at the maximum possible speed allowed by the SMTP server antispam restrictions. Here’s the meaning of each option:
- Pause between messages: the number of seconds elapsing between message sending.
- Pause between blocks: the number of messages elapsing between each block of messages.
- Messages per block: the number of messages sent in each block
- Timeout: the maximum number of seconds after which the message sending is aborted
- Connections: the maximum number of simultaneous connections, meaning the number of messages simultaneously sent*.
- Further attempts in case of error: If the SMTP server or the recipient’s server (for a direct send) doesn’t accept the message, the software can wait a certain number of seconds and retry sending the message one or more times.
- Pause between attempts: the number of seconds of delay before retrying to send an unaccepted message.
The right configuration cannot be set before a few attempts, verifying the number of messages that actually get delivered. To simplify the settings, some Suggested settings are available. They might not be optimized for your connection but can be considered a good starting point to get the best configuration.
Warning: Distribution lists can contain invalid e-mail addresses, or some e-mail servers may be temporarily inactive. Therefore, when using lists that contain a great deal of addresses it should be considered normal and inevitable that, despite the chosen sending mode and the settings, not all messages will get delivered and a certain percentage will return an error. In such case it will be possible to try to complete the sending operation at a later time using the history functions.