The sustained rate at which you can send email messages is based on many factors:

1. Shared vs. dedicated
2. Server power (CPU cores, memory and disk speed)
3. Email sending program used
4. Use of SMTP pipelining
5. Use of SSL/TLS
6. Proper use of concurrent connections
7. Network speed between the sending program and LuxSci
8. Message size
9. Recipient server and DNS performance
10. Blacklisting and greylisting
11. Recipients/message
12. Message encryption
13. Other message processing
14. Throttling

The "maximum sending rate" (msgs/hr) for Spotlight Mailer is a theoretical maximum rate that messages can be sent from LuxSci's Spotlight Mailer under the same optimal sending conditions: very small (1 KB) messages, all to the same recipient domain, where there is no blacklisting or greylisting, where encryption is not needed, and where SSL is not used. Spotlight mailer is has an extremely fast connection to the SMTP server, uses SMTP Pipelining, and uses 4 concurrent connections.

Actual throughput with Spotlight Mailer will be less based on the other factors which affect the sending rate: SSL, Message size, Recipient server and DNS performance, blacklisting and greylisting, any additional processing being performed (e.g. anonymization or encryption), and others use of the Spotlight Mailer system (unless you have a dedicated Spotlight Mailer install)

Sending at a consistent rate for a long period of time. E.g. 20,000 messages/hour for minutes or hours. Sustained rates are relevant when sending an email marketing blast to a large subscriber list.

A "burst" refers to sending a bunch of messages in a very short time; e.g. 25 or 50 messages within a second or two. Burst differs from "sustained" in that when you are not "bursting" you are sending one or a few messages here and there ... infrequent sending. Bursting is relevant for transactional email messages when you are sending them "as needed" but require the ability to send many at once should that need arise, as it will.

Dedicated servers will generally be faster. On shared servers, you must share the server's sending capacity with others and thus you do not have control over the capacity available to you at any particular time.

More powerful servers can handle more concurrent connections and thus give you higher sending rates. The number of CPU cores is the primary factor governing performance; however, memory and disk speed are also important.

Different email marketing/sending programs have different capacities for how efficiently they can send high volumes of email. Simply switching from one program to another can increase your throughput significantly.

LuxSci Spotlight Mailer is a very efficient program.

Use an email marketing program (like LuxSci Spotlight Mailer) that supports SMTP Pipelining. With this feature, the program opens a single authenticated connection to the server and sends multiple messages in succession over that connection. This is significantly faster than opening a new connection and logging in again for every single message to be sent.

LuxSci Spotlight Mailer uses SMTP Pipelining.

SSL is extremely useful for security and for the protection of your username, passwords, and message content. However, when using SSL, your email sending program and your server must perform work encrypting and decrypting all of your messages. This overhead will slightly slow down your rate of sending.

If your sending program can open 2 connections to our SMTP servers at the same time and send two messages at once, then your sending rate can generally be up to twice as fast. Depending on how powerful your server is and how slow your network connections are, you can use more and more concurrent connections to achieve higher and higher sending rates. Combined with SMTP Pipelining, an appropriate number of concurrent connections goes a long way to maximizing your throughput potential.

The recommended number of concurrent connections for best results in sustained sending is given for each server type.

Note, that if you use more concurrent connections that is recommended, then you are likely over-working your server. That results in your sending rates actually getting slower. Stick to the recommended number of concurrent connections.

Your messages must be transmitted from your email sending program to our servers. The speed of your network, any packet loss, and the distance between your sending computer and our servers can significantly impact the maximum rate that you can send messages.

For example, LuxSci Spotlight Mailer sends from a server right next to your outbound email servers and thus network speed is not a factor. For someone connecting from outside of LuxSci or internationally, the speed can slow down significantly.

Like network speed, the larger your messages are, the more time it will take to transmit them from your email sending program to our servers. For example, on a fast network, increasing message size from 1KB to 1MB decreased throughput by 50%. The actual impact of size will depend greatly on your network speed and other factors.

In order for our servers to deliver messages to your recipients, the servers have to (a) look up where to deliver the messages to (DNS), and (b) talk to those servers to deliver the messages to them. If the DNS lookup as slow or the recipients are in domains that no longer exist, this step can take a while. If the recipient's email servers are overloaded, on a slow network, or are having other issues, then the delivery phase can be slow.

Delivering many messages to recipients with these issues will slow down your entire sending process... as other messages have to wait for the slower ones to be sent.

If your email content or sending patterns have gotten your server blacklisted or greylisted, then delivering email messages to recipient servers that are now blocking you or deferring you can slow down your delivery rates.

This can also cause a backlog of messages that are waiting to be accepted by these recipient servers. The need to Retry the backlog slows the process of delivering all other messages (though it does not block their delivery).

Most email marketing and transactional email messages are sent individually to each recipient. This allows easier tracking of opens, views, etc. However, if you send each message to many recipients (e.g., 100s of recipients), then your sending program has significantly fewer messages to deliver to our servers. The delivery of your messages to our servers can happen 10s or 100s of times faster than if you sent in the usual one recipient/message pattern.

Additionally, if each message contains only recipients in a specific domain, then actual delivery to these recipients can be expedited by this efficiency. E.g. If you are sending to 500 AOL users, instead of sending 500 individual messages, send one message with all 500 AOL users listed as "BCC" recipients. Delivery can be almost 500 times faster.

It takes some system resources (CPU cycles and network requests) to auto-encrypt outbound email messages. If all of your messages need SecureLine outbound encryption, this will somewhat detract from the maximum delivery rate. The impact will depend on many factors such as which encryption modes are used, if DNS additional lookup need to be made, etc.

If you are using SMTP Anonymization or other email processing features that come with High Volume Secure Sending (e.g. content scanning, recipient restrictions, size restrictions,etc.), this processing will affect your maximum sending rate.

LuxSci has features that can be used to rate limit the processing of outbound email. This is usually used when "warming up" IP addresses to assist senders in sending slowly and establishing their IP address reputation.

This rate limiting is on, your maximum sending rate will be capped by this process.