Maximizing Delivery Speed and Reliability for Large Scale Email Marketing
Many customers want to send millions of marketing messages within a short timeframe without getting blocked by recipient ISPs to maximize the number of recipients and the conversion rates on these messages.
This is a common scenario that we see, often from customers who have been using another costly provider, where delivery is sluggish or where messages are blacklisted or greylisted by their recipient’s systems.
Here we will share our standard prescription for solving this delivery dilemma once and for all. There are multiple factors involved, each of which will contribute to success.
1. Use a Dedicated Server for Large-Scale Email Marketing
When sending out large-scale email marketing campaigns with thousands or even millions of recipients, it is important to use one (or more) dedicated servers.
A “dedicated server” means
- The server and its resources belong solely to the organization. No other customers share these resources.
- The server will have a dedicated IP address.
Both of these are exceptionally important:
No sharing of capacity:
By not sharing the server with other customers, the entire power of the server is available to the organization allows messages to be sent as fast as possible. In a “shared” system, the actual sending speed can be degraded by the usage of other customers.
Dedicated IPs
The IP address of the server is the address that ISPs see all the email as originating from. The reputation of this IP address (e.g. how much “spam” is seen coming from it) plays a critical role in determining message deliverability. By having a dedicated IP address, the server’s reputation and delivery power are a function only of the organization’s sent marketing messages.
Contrast to a shared environment where a bad apple customer sharing the same IP address can send spam and diminish that address’s reputation causing the organization’s email to be delayed or denied as a result — at least until the issue is detected and remediated.
2. Use SPF and DKIM
When recipients’ mail servers evaluate the organization’s email marketing messages to determine how “spam-like” they are and whether they should be let through to their inboxes, many factors are considered. The first is the reputation of the sending server’s IP address (discussed above). They also look at the message contents to see how much those look like other known spam messages. Tools like those are built into Secure Marketing to discover these spammy words and allow for message revision.
However, most spam on the internet comes through using forged email addresses as the senders. As a result, ISPs highly value any way to validate if a message is forged or authentic. Using “signatures” in messages to prove they are not forged and come from authorized servers enhances their legitimacy and message deliverability.
To do this, set up SPF and DKIM for the domain to designate the email marketing provider as an authorized email sender. See also seven misconceptions about DKIM in the fight against SPAM.
3. Use Multiple Servers to Increase Speed and Volume
If sending a large-scale email marketing campaign within a short time frame, you may be hampered by sending through a single server. Many factors affect sending rate. A big one is the server size.
A single server can only process so many concurrent connections and messages, only has so much network throughput, and thus will limit how many messages can go out per second. This can be mitigated by either (a) getting a more powerful server or (b) by using multiple servers.
While using a larger server is simpler and works in many situations, using multiple servers is often recommended for customers with very large sending volumes. In terms of speed and volume, multiple servers permit more network throughput and disk I/O throughput than you would usually get simply by beefing up a single server. In addition, they come with a smaller price tag (two cheap servers are often the same price or less expensive than a single server that is twice as powerful).
A multiple-server scenario is more scalable and allows organizations to adjust capacity by adding and removing servers from the system. E.g., add more near the holiday rush, and dial back for the rest of the year. It is usually more difficult to upgrade/downgrade a single system, and that also, when possible, usually involves downtime and may change the IP address on which you have carefully built up an excellent reputation.
4. Use Multiple Servers for Failover and Reputation
There are several additional reasons why multiple servers are preferable to a single powerful server when sending large-scale email marketing campaigns.
Server Failure
If using multiple servers and one fails, timely marketing messages can still be delivered through the other servers while the failed one is repaired.
IP Reputation
The more email that comes to an ISP (like Yahoo) from a single IP address, the more suspect that email can appear to be. There will also be a larger number of complaints against the mailings as the number of messages coming from an IP increases. Finally, some IPs will throttle messages from the IP when the quantity being delivered reaches some threshold.
By splitting the marketing emails over multiple servers and thus multiple dedicated IPs, it proportionally decreases the amount of email coming from each IP and thus enhances the reputation and deliverability of email from all of your IPs. The maximum delivery rate of messages can also be increased to ISPs that rate limit email delivery (because your email is not coming from just one location).
5. Warm Up IP Addresses Before Sending Large Scale Email Marketing Campaigns
Running a race without warming up leads to injury. It’s similar to email marketing.
Starting to send email marketing messages on a brand new server rapidly is likely to impact email deliverability negatively. Imagine the scenario from the point of view of the recipient’s ISPs (e.g., AOL or Gmail, or Yahoo). They have gotten little or no email from the new IP address, and suddenly they are inundated with email. They will think that the machine has been taken over by a spammer hoping to get out as many messages as possible before being caught.
To avoid this, warm up your IP address(es). Like stretching, it’s easy but takes a little time and is well worth it:
- Start small. Send small batches of emails to selected subscribers (e.g., segments)
- Ramp up. Over a few weeks, gradually increase the volume of email coming from servers from an initial modest amount (e.g., 1000s a day) to close to target amounts (tens of thousands or more per day).
- Be consistent. Be consistent with message wording and content. If the messages are consistent and not very spam-like, it will help build your IP reputation.
By ramping up like this, it will not catch the attention of IPs, and they will accept initial modest email blasts. They will allow the messages through and see that people are not complaining about the email (e.g., not marking it as spam). As those initial sends go well, they will allow larger and larger sends as the reputation of the IP address builds from “unknown” or “solid.”
What about a “pre-warmed IP?”
A pre-warmed IP is when an email marketing provider has an IP that “already has a good reputation” so you can “just get going.”
How is an IP pre-warmed? It is done when some other company uses it for sending their email. If that company does a good job and builds a good reputation and then doesn’t need the IP anymore, it can be assigned to another company and maybe sending can start without “warming up.” Maybe.
But even in this scenario, be wary:
- How good is the reputation of that IP?
- What were they sending on it? If it is really different from what the organization is sending, will that affect how “warm” it appears to be with respect to its messages?
- Even if the reputation was good, what volume were they sending per day and what volume can be send that won’t be flagged as spam?
Generally, it’s difficult to know the answer to any of these questions, especially #2, it is always best to “start slow” and warm up the IP yourself, even if it was “pre-warmed.” This can only be to your benefit... like stretching.
