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8 Ways to Maximize Email Throughput: Send More Email, Faster

Tuesday, September 5th, 2023

Sending high volumes of email messages is more complex than sending a quick message to a colleague. To reach a large contact list in a timely manner, it’s essential to understand ways to maximize email throughput. In this article, we lay out eight best practices for sending more emails faster.

person sending emails on laptop

1. Use Concurrent Connections

When sending an email message, the emailing program connects to the servers, establishes its identity, and passes the message through. When sending emails in bulk, connecting to the server can take up a lot of time. For example, if you send 1,000 messages, the program must connect to the server 1,000 times. Many sending programs can be configured to make more than one connection at a time. If you make ten connections simultaneously (e.g., concurrently), you could send those messages about ten times faster. That is a significant speedup.

However, you don’t want to make too many concurrent connections. The more connections you make at once, the harder the server must work to process the mail. The server will become overloaded at some point, and the average time to send a message will increase. You want to avoid pushing the server to the point where it struggles to keep up with sending, as that will only make it operate slower. Instead, use a modest number of concurrent connections to take advantage of parallel sending and allow the server to efficiently process all the messages.

We recommend keeping concurrent connections to ten or fewer if you use public cloud servers and share capacity with other bulk senders. Single dedicated servers can support between 20-30 concurrent connections (or more depending on the factors discussed below), and dedicated server clusters can support as many as you need (depending on how large a cluster you have).

2. SMTP Pipelining

The next way to maximize email throughput involves utilizing SMTP pipelining. First, let’s look at the regular way messages are sent via SMTP:

  1. Connect to the SMTP server
  2. Establish SSL or TLS encryption, if configured
  3. Authenticate the sender’s identity and permission to send
  4. Upload the list of recipients and message content
  5. Disconnect

When sending small messages, the time taken by steps 1, 2, 3, and 5 is very significant relative to the time it takes to upload the message data. With SMTP pipelining, the connection is reused for successive messages. For example, when sending three messages, the process looks like this:

  1. Connect to the SMTP server
  2. Establish SSL or TLS encryption, if configured
  3. Authenticate your identity and permission to send
  4. Message 1: Upload the list of recipients and message content
  5. Message 2: Upload the list of recipients and message content
  6. Message 3: Upload the list of recipients and message content
  7. Disconnect

Not repeating the connect-authenticate-disconnect steps for every single message saves time and sends messages faster. SMTP pipelining should always be used if supported by your email-sending program and outbound email service.

3. Multiple Recipients in One Message

Imagine sending the same message to 1,000 recipients. If you send these one at a time and it takes one second to process, it takes almost 20 minutes to send 1,000 messages. Instead, if you include all recipients in the BCC line of a single message, it will take only about 1-2 seconds to upload the message to the server (though it will still take the server some time to deliver it to those recipients).

Sending messages to multiple recipients using BCC allows you to upload messages to the server much faster.

There are two downsides to this method:

  1. The received message may appear more SPAM-like since the recipient would not see their email address as the “To” recipient. BCCs are more SPAM-like than messages individually addressed (because it is so much easier and faster to send this way).
  2. A single message sent to 1,000 recipients may take longer to be delivered as the mail server will not generally parallelize delivery to the recipients but will process them sequentially. This may not be important if the delivery time is not time-sensitive.

LuxSci’s Secure High Volume service allows you to send to up to 1,000 recipients in each message. Customers with dedicated servers and clusters can have this limit increased to suit their business needs.

4. Smaller Messages are Better

A significant factor in maximizing email throughput is reducing the time it takes to upload each message to the server. To see the difference, let’s look at an example — sending a one-megabyte PDF to 1,000 people in 1,000 separate messages.

Case 1 – The PDF is attached to the message, and it takes ten seconds to upload the large message to the mail server. It takes 10,000 seconds (almost 3 hours) to send 1,000 messages with the attachment (unless you use some of the other strategies for maximizing throughput mentioned above).

Case 2 – The PDF is placed on a website, and a link is included in each message. The email message is only ten kilobytes (100 times smaller than in Case 1) and can be sent about 100 times faster. That’s less than 2 minutes without any other optimization.

As you can see from the example, it is best to remove images and other attachments from bulk messages to decrease the message size. Images can be hosted on a website and displayed in the message by linking rather than including the image content every time. Attachments that are not sensitive can be similarly hosted on a website and linked to. Reducing the size of your email messages significantly impacts sending speed and helps maximize email throughput.

5. Clean Mailing Lists are Important

Email messages should only be sent to contacts who have opted into communications or with whom you have established business relationships. These are the standard terms for using any reputable bulk mailing service.

Even if you follow the rules, mailing lists get stale as people change addresses, domain names go defunct, etc. Removing invalid addresses and only sending messages to clean mailing lists is imperative. Why?

  • Bad Domains. Sending an email to an email address whose domain name is no longer valid can delay sending while the program determines if the domain is bad. Determining that the domain is good and the email should be delivered takes less time. The delay caused by expired domain names can slow down your sending.
  • Defunct Addresses. Sending emails to invalid email addresses looks like spamming. Recipient servers like Yahoo!, AOL, McAfee, etc., are very sensitive to the number of messages that come through to defunct email addresses. If they see a lot of these, they will either block emails or slow down the rate at which they process them. This will result in more delays and potential non-delivery to valid recipients.
  • Waste of Time. Attempting to send messages to invalid recipients also wastes time and money.

You should take advantage of tools available to track what recipient email addresses are failing and actively remove them from your mailing lists.

6. Insecure Sending is Faster than Secure

While encrypting your username, password, and message contents is always recommended, this encryption will slow down email sending. It requires extra processing by the server and the sending machine. Using encryption also requires more bandwidth to transmit the data.

So, if you want to maximize email throughput, we recommend not using TLS or SSL when connecting to your bulk SMTP server. However:

  • Ensure that the username and password used to authenticate the message sending is not used for anything else. It is not your administrator user, the password is not one of your “standard” passwords, etc. You must assume that this username and password could be compromised.
  • Do not grant this user any permission except for sending emails. At LuxSci, you can restrict it from using the web interface and any other services.
  • Change the password often- weekly is recommended.
  • Use tools to check that no one else is using this credential to connect to your SMTP service. LuxSci provides alerts and reports about logins, which you can use to be sure that no one else is accessing this user account.

If the credentials are compromised, and you have followed these guidelines, the worst thing that could happen is that someone could send email through your account until you change the password or hit your sending limits.

7. Use an Appropriate Email Program

Many programs that are good for regular email sending are terrible for bulk email messages. Don’t bother trying to use Outlook, Thunderbird, Apple Mail, Gmail, and similar programs to send high volumes of email if you are interested in sending speed or efficiency. Why? Such programs:

  • Generally, do not support concurrent connections
  • Might not support SMTP pipelining
  • Cannot efficiently handle large mailing lists (more than hundreds of recipients)
  • Get bogged down and can be very slow when sending many messages

These programs are not designed or optimized for high volume sending. Instead, use a program explicitly designed for bulk mailing, like LuxSci’s Secure High Volume or Secure Marketing, which supports maximizing outbound email throughput in the ways outlined above.

8. Increase Capacity

If you try the above solutions and still need faster delivery times, you may need to increase your outbound server’s sending capacity. At LuxSci, we offer tiers of capacity that allow you to create a fully custom solution to meet any throughput requirement:

  • Shared – Your account shares a single server with multiple other accounts. The server’s capacity is shared, and your sending throughput (i.e., maximum concurrent connections, maximum recipients/month, etc.) is restricted to maintain enough capacity for other customers. Your outbound IP reputation is also shared with others.
  • Dedicated – A dedicated server gives you complete control over the sending server resources and IP address. You get all the capacity to yourself and thus can attain a much higher throughput. Your IP address is not subject to other customer’s actions to help you maintain a good reputation.
  • Cluster – A dedicated server cluster may be a good solution if you need to send many messages very quickly. It consists of two or more outbound servers behind a load balancer. The more servers you put in the cluster, the higher your throughput can be. Another benefit of a dedicated server cluster is having multiple sending IP addresses for reputation management and failover to make your sending more resilient.

Which option is best? It depends on the number of recipients you want to reach per month. Also, if you need to send to large numbers of recipients in a very short time frame, you may need a dedicated or cluster solution. LuxSci’s team of email experts can help design the correct configuration to suit your throughput requirements. Contact us today to get started.

Tags: bcc, concurrent connections, dedicated server, email list clean up, email list hygiene, email spam, high volume, multiple recipients, outbound email, secure high volume, secure marketing, smtp, SMTP Pipelining, ssl, tls
Posted in Business Solutions, Dedicated & Cloud Servers, Email Marketing, LuxSci Library: The Technical Side of Email
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Email Marketing Metrics: 5 KPIs for Data-Driven Marketers

Wednesday, May 17th, 2023

Open rates only offer a small glimpse into the success of your email marketing campaigns. To determine whether your campaigns successfully drive engagement and behavior, diving deeper is necessary. In this article, we go beyond the basics to look at other email marketing metrics that can help you determine the success of your campaigns.

data-driven email marketing

Click-Through Rate (CTR)

One way to tell if your email content engages your audience is by looking at the click-through rate or CTR. Instead, looking at your messages’ click-through rate can tell you more about how successful the campaign is. The click-through rate can be calculated by dividing the number of total clicks (or unique clicks) by the number of emails delivered.

 This metric tells you how successful the message content is and whether the recipients find the content engaging. Many split tests are designed to find new ways to get more clicks in your emails, and the click-through rate is an essential metric to determine success. Clicks are significant because they often lead to conversions.

Conversion Rate

For most marketers, the conversion rate is the most vital metric to track. The conversion goal you are tracking may change from email to email. For example, the goal of one campaign may be to increase app downloads. In another, the goal may be to increase appointment sign-ups. Whatever your goal, to track the conversion rate, you compare the number of people who completed the desired action to the number of emails delivered. 

To measure the conversion rate of your emails, you may need to integrate your email platform with web analytics. You can do this by creating unique tracking URLs for your email links that identify the source of the click as coming from a specific email campaign. Tracking the source is incredibly important for understanding the ROI of your email campaigns.

Bounce Rate

It’s imperative to keep an eye on your bounce rate. The bounce rate measures how many emails were delivered to the recipients’ inboxes. Bounces can either be soft or hard. Understanding why an email failed to be delivered can help you improve your lists for future sends.

Soft bounces result from a temporary problem with a valid email address, such as a full inbox or a problem with the recipient’s server. The recipient’s server may hold these emails for delivery once the problem clears up, or you can try to resend the message manually. 

Hard bounces result from invalid, closed, or non-existent email addresses. These emails will never be successfully delivered. You should immediately remove addresses that hard bounce from your email list because internet service providers (ISPs) use bounce rates to determine an email sender’s reputation. Keeping your email lists clean is essential to maintaining email deliverability.

Unsubscribes

Similarly, you should be tracking who is unsubscribing from email messages. Seeing a small number of unsubscribes from your email campaign is expected. The average email campaign unsubscribe rate is about 0.2%. Nevertheless, tracking unsubscribes on a per-campaign basis is helpful to ensure your content is hitting the mark. If your unsubscribe rate jumps above the average, it may be time to re-evaluate your content or clean up your lists. Unsubscribing indicates that the recipient did not find your messages engaging, and you should remove any contacts who unsubscribe from future marketing messages. There are also legal ramifications for failing to comply. The CAN-SPAM Act requires companies to honor all opt-out requests and enforces penalties for noncompliance. 

Spam Complaints

Spam complaints can also affect the future deliverability of your emails, so it’s crucial to track who is marking your emails as spam and remove them from your list. Spam complaints are delivered to ISPs, and receiving a lot of them could impact your deliverability and sending reputation. If you aren’t tracking these requests, you could be emailing people who do not want to be contacted by your company.  

Conclusion: Implement Data-Driven Email Marketing Today

Move beyond top-line email marketing metrics to take your email marketing expertise to the next level. You can better engage patients, drive behavior, and improve outcomes by using data-driven email marketing techniques. Contact LuxSci today to learn more about how our HIPAA-compliant email marketing software can help you achieve results.

Tags: click tracking, conversion rate, data driven email marketing, email analytics, email deliverability, email engagement, email list clean up, email list hygiene, email marketing, email marketing metrics, metrics, patient engagement, precision nudging
Posted in Email Marketing
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Email List Hygiene: 5 Best Practices for Cleaning Up Email Lists

Tuesday, August 2nd, 2022

When sending emails from a new server and IP address, we always stress the importance of warming up the server to prevent emails from being flagged as spam. One critical step of the warm up is sending small batches of messages to email contacts that are likely to open and click on the content. Sending to clean email lists helps build a positive IP reputation and will improve email deliverability over time. This article explains the basics of email list hygiene and how to clean up email lists.

email list hygiene

What is Email List Hygiene?

Email list hygiene involves removing ineligible contacts from lists and adding new addresses with proper permissions and consent. Good email list hygiene contributes to good email deliverability and engagement. It also prevents emails from being marked as spam because all recipients have agreed to receive email communications. Here are our tips for cleaning up email lists:

How to Clean up Old Email Lists

1.     Remove Role Accounts

We don’t recommend sending emails to addresses that are groups or aliases that support a specific business function. These include addresses like:

Spammers often scrape these addresses off websites and send them unsolicited emails. To successfully warm up a new IP, it is essential to differentiate sending patterns from spammers as much as possible.

2.     Remove Inactive or Incorrect Email Addresses

Most mailing lists contain old email addresses that are no longer active. Removing these addresses before warming up a new mail server is essential. Spammers often purchase lists that contain a high proportion of inactive emails. Sending to many inactive addresses may cause the server to be flagged as spam. Also, check for and correct common misspellings and typos, for example, “gamil.com” vs. “gmail.com.”

If working with a large email list that hasn’t been contacted in a while, it may be worthwhile to use a paid tool to run these verification checks and remove bad email addresses.

3.     Review Email Permissions

Before sending a campaign, review how the email list was collected. Sending unsolicited emails is an excellent way to be marked as spam. If marketing communications are planned, ensure the contacts have explicitly agreed to receive marketing messages. The CAN-SPAM Act regulates how marketers can use email to communicate with prospects. It’s essential to confirm that the list was not collected in a way that violates those terms. In addition, never send to a list purchased from a third party, as that violates the CAN-SPAM Act and can lead to massive financial penalties.

Sometimes, the origins of an email list may be unknown. In this case, running an opt-in or re-engagement campaign is a good idea. This gives users the opportunity to resubscribe to the mailing list and reengage with the brand. Only sending emails to people who have opted in increases the likelihood they will engage with future emails. Remove contacts from the list who do not respond or opt-out from future communications.

Ongoing Email List Hygiene

Setting up a schedule to maintain email list hygiene is crucial to preserving IP reputation. It takes ongoing work to support list hygiene. Including email list cleaning tasks in campaign set-up and performance reviews is essential to ensure campaigns are delivered to the recipients.

4.     Remove Bounces, Spam, and Unsubscribes

After every campaign, remove addresses that have unsubscribed or bounced. Most email marketing tools will automatically remove unsubscribes but reviewing the feedback is essential. If many people unsubscribe even after list clean-up, review the email contents to ensure they are relevant and not spammy.

Likewise, even verified subscribers may report emails as spam instead of clicking on an unsubscribe link. We recommend removing contacts who have marked emails as spam because it is a clear indicator that they no longer want to receive these types of emails.

Continuing to email users who have unsubscribed is a CAN-SPAM violation with penalties in the thousands of dollars. Bounces are not usually removed automatically by email programs. Marketers should review the list of bounced emails after every campaign is sent and remove bounced addresses to keep the list clean. Lists acquired from spammers often contain many email addresses that will bounce, so avoiding sending to bounced addresses is recommended.

5.     Set Up Double Opt-In for New Subscribers

Even if the original list was not collected according to best practices, setting up validation procedures for new subscribers can help ensure that only people who want to receive emails will get them.

The best way to validate email subscribers is by setting up a double opt-in process. By “double opt-in,” we mean that when someone signs up for an email list, they are sent another email requiring them to confirm the subscription by clicking on a link before being added to a list. This helps ensure that only people who want to receive brand communications will be added to the lists.

Conclusion

Cleaning up email lists can initially be time-consuming. Setting up the proper procedures and reviewing existing lists regularly can help maintain proper list hygiene and improve email deliverability.

Tags: deliverability, email deliverability, email list clean up, email list hygiene, email spam, IP warm up, unsubscribe, warm up
Posted in Email, Email Marketing
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