Email deliverability best practices for large volume senders

For large volume senders, it is vital to know that the more emails you send, the more challenging it becomes to ensure maximum inbox delivery. In order to efficiently manage your reputation, there are a few key email deliverability best practices you need to understand and apply:
  1. As a high volume email sender, a dedicated IP is most likely your best option for deliverability:

Your Email Service Provider (ESP) will give you a solid idea of whether your allocated Internet Protocol addresses (IP) should be dedicated or rather shared. If allocated a shared pool of IP's, then ultimately you are sharing your sender reputation with other senders on those IP's; and your email delivery is subject to their sender behavior. As you do not know who they are or what they are doing, your reputation becomes vulnerable and at risk. Therefore, as your sending volume goes up and you begin to rely heavily on email, (and where your revenue is dependent on email) it is imperative to have a dedicated IP to ensure that your reputation is a function of your own sending practice rather than someone else’s. It’s basically the same decision as accepting the class average on a test you need to do well in, rather than preparing and writing the test yourself.

Typical symptoms of a shared IP system are inexplicable drop offs in your delivery [when someone else on the pool damages this IP reputation] and slow sending times [due to concurrent campaigns being sent by multiple users].

  1. Know whether dedicated IP's are right for you:


Dedicated IP's require some maintenance to be good deliverers of email. In order to retain its reputation, an IP needs a minimum quantity of mail being sent from it each month or so. The reason for this is that incoming mail servers often look up the IP on inbound mail and reference that against a range of metrics, such as:

    • How much email that IP sends.
    • Whether it traditionally sends opt in email or not.
    • Whether the IP is currently on a blacklist.
    • What the IP's score is on a range of metrics such as Cisco SenderBase and Returnpath SenderScore.

 The better these metrics look, the better your chance of always inboxing. The only way to build a good sender reputation is to consistently send good opt-in email.

Should you not send enough email to establish a reputation with the various gatekeepers, monitoring services such as Returnpath’s SenderScore will leave your IP without a sender reputation (Neutral). Although this doesn't necessarily count against you, a positive one will result in an improved inbox email delivery. It is for this reason that your sending frequency and volume should be considered strategically to maintain this reputation over time – especially in cases where you're sending mass mail over multiple dedicated IP's and some IP's are used more than others or have irregular sending spikes.

The basic rule of thumb is that if you are sending at least 20 000 emails a month that’s enough to maintain a dedicated IP. Anything less than that will mean you don’t cash in on the benefits of a dedicated IP, as you will not build a consistent sender reputation. If the latter is the case, we’d recommend going for a shared IP solution, however be certain to have your ESP declare which IP's you are being allocated so that you can check the IP reputation before sending. See article on dedicated versus shared IPs for optimal email marketing to find out more.

  1. Specific email jobs might call for multiple dedicated IP's:

If you are sending high volumes of bulk email marketing with time-sensitive transactional mail, using multiple dedicated IP's for specific email jobs should definitely be something to consider. For an example, if you are sending bulk marketing mail and transactional mail over a single dedicated IP, your time-sensitive transactional mail could get queued behind a large batch marketing mail, and if you receive a high complaint rate on your bulk marketing mail, your time-sensitive transactional mail deliverability gets injured. Also, if you have a lapsed customer database in addition to newly signed up customers, you ideally want to consider using separate dedicated IP’s to service each database as older lists produces a higher bounce rate compared to newer sign-ups, and although you want to send messages to all of them, if that IP manages to get blacklisted, your newer sign-ups - the more engaged recipients and potential customers - won't receive your mail.

  1. SPAM monitoring services identify large volume senders faster:

It is essential to realize that sending 10 000 emails versus sending one million emails is an entirely different challenge. Large volume senders are much easier for monitoring services to identify as there's naturally a lot more signals from recipients providing feedback about what they think of their mail. As a result, it exposes you to a lot more scrutiny from spam filters who will either categorize you as a large reputable sender, or a spammer. It is critical that your reputation is flawless and constantly maintained; if it’s not, you are inescapably at risk of getting caught in spam filters. Once classified as a spammer, it is an uphill battle to reverse the damage and repair your reputation.

  1. Countless statistical signatures efficiently spot spam content:

Always make sure that the content of your mail has been checked by content checker tools, as your content’s spam score could be problematic without you being aware of it. Advanced Bayesian based email filters like razor2 and Cloudmark use particular rules and are constantly uploading countless statistical signatures to identify email content as spam. In a single email sent, these content checkers analyze many aspects, including but not limited to: sender address, email source (html and text), links, words, images, text to image ratio etc. If your content gets indexed and you repeatedly send out the same content, red flags will be raised and it is only a matter of time until you get blocked. Using content checker tools like SpamAssassin will give you guidance on where you may be going wrong in your email content. However, if you’re interested to know more about how Razor2 and Cloudmark operate, read more about it here.

  1. Switching ESP's means switching IP's and rebuilding sender reputation:

As you increase your sending volume, switching to a more scalable ESP solution might be necessary and it is important to understand that switching ESPs also means switching to new IP's and having to totally re-build your sender reputation. The switch can be logistically tricky, but if done correctly it can be extremely rewarding in the long run. The advisable way to do this is very slowly – Essentially you are warming up your IP by staggering sends to smaller segments in your database of roughly 10000 subscribers each, over a few weeks. Do not make the jump in a day. It is normal to see a drop in delivery % when changing ESP's; however the more aggressively you mail, the bigger that drop off is, which can often result in migrations having unforeseen impact on business. The good news is that any decent ESP will have a migration process, and staff to help you manage this, free of charge. Contact us  if you’re unsure of this and we’ll be able to advise you on the best approach.

Your ESP needs to not only handle high volume traffic but also to ensure your messages are delivered to the inbox. When choosing an ESP it is important to ask questions about the infrastructure, like how they handle inbox deliverability, and warming up IP's and throttling etc. Always provide your ESP with detailed information about your mailing volume and mailing frequency, what content you’re sending, and the exact state of your database. They will be able to advise you of anything risky in terms of what you are sending, who you are sending it to, when you send it, and assist you best according to your needs.Always make sure you check whether the ESP in question provides the best delivery practice, technical support, bounce back handling and other advanced analytics. A few warning signs that an ESP is not for you:
  • You are a large sender, and an ESP offers to import your database immediately with zero consultation.
  • If your ESP does not offer account management to large senders.
  • If your ESP doesn't have a live monitoring and management program of blacklists, along with Senderscore, Cisco Senderbase and Cloudmark.
If anything is unfamiliar to you, we advise you ask these questions of your provider and make sure they have an answer ready.  Assuming that your chosen ESP ticks all the above boxes, settle on an appropriate migration plan and timeline, and go for it!