First some definitions: delivery rate and deliverability. These are not the same: delivery rate refers to the mails reaching the recipients ISP (Internet Service Provider for instance Gmail, Outlook, Apple) relative to the emails sent. Deliverability concerns the number of emails placed in the inbox.

Delivery rate

Delivery rate is usually managed by 2 factors. Maileon manages this in technical terms. The other factor is practicing proper list hygiene: processing complaints, bounces and unsubscribes correctly, ISP’s monitor this and this monitoring influences your sender reputation. In standard installations, your Maileon account handles these properly. If you are migrating and want to know more about the state of your existing mailing list(s), make sure to ask about our AddressCheck feature to provide valuable information on the status of your subscribers. This feature is able to detect harmful addresses such as spam traps, bots and temporary addresses before they harm your sender reputation.

Sender reputation

Next relevant topic is sender reputation, either based on IP or (sub-)domain. IP reputation is managed automatically by Maileon and the pool of thousands of sending IP addresses. Domain reputation is based on the (sub)domains you use for sending out mailings. 

You can manage your domain reputation by practicing good list hygiene and improve the deliverability with the tips mentioned in this article. You need both good IP and domain reputation to effectively deliver your email.

Typically, your sending subdomain is delegated to Maileon by implementing DNS records. Domain Name System (DNS) is generally a sort of address book for your web domain, where for instance the connections with your web hosting and email service are stored. Because of DNS a web browser shows your website on www.yourdomain.dom and delivers email to And in this case, you set up DNS records to delegate a subdomain like to Maileons servers so we can set this as a sender domain.

Subdomain setup

Subdomain delegation is an industry-standard setup method, with the benefit of having the subdomain visibly related to your main domain while it enables Maileon to manage IP reputation. Using a separate subdomain for sending with Maileon (such as attributes to a better manageable domain reputation and does not interfere with sending regular emails. Maileon is then also able to handle the other aspects of authentication & infrastructure for you (such as SPF, DKIM and DMARC) by industry standards.

Improving deliverability

Most of the mentioned topics above manage delivery rate, but what if you want to improve deliverability and reach the inbox instead of a spam folder? In summary these are the relevant topics:

  • Content
     Make sure your content is relevant to your recipient. If they gave permission to email them, that’s a good first step. But it does not ensure relevance. Consider testing and personalizing content to get the best results on your KPI metrics: opens, clicks and conversion (in short: engagement) still matter on this topic. See more on the topic of engagement below
  • Subject lines

Using a proper subject line obviously attracts opens and positively influence (future) deliverability. Of course, refrain from using spammy keywords and don’t go to crazy with special characters, emoji and using ALLCAPS. Maileon gives tips on using a good subject line in the mailing editor.

  • Subscriber behaviour
    This is in technical terms handled mostly by Maileon. Subscriber behaviour refers to:
    1. spam complaints triggered by recipients who feel that you don’t have permission to email them, you were mailing too frequently or less relevant/unwanted. Being relevant is becoming increasingly important lately.
    2. feedback loops allow a sender to receive reports on recipients marking email as spam or junk mail. To maintain a clean email list, you can then suppress, or prevent, unwanted messages from appearing in that particular inbox. Your Maileon account is automatically handling feedback loops.
  • Subscriber engagement
    Your KPIs (opens, clicks and conversion) indicate the engagement of your recipients. Also mailings that are deleted without even opening are attributing to this metric. ISP algorithms factor in engagement to automatically move mailings into spam or promotional tabs or folders instead of inboxes. Other topics to improve subscriber engagement with:
    1. TINS (This is not spam): if an email does get into spam folders, it’s very valuable for these contacts to move the mailing to their inbox and hereby marking the mailing as NOT spam.
    2. Allowlist, whitelist or add to contact list refers to contacts actively approving you sending them email

ISPs generally take subscriber engagement very seriously. If your email generates positive interaction and engagement, it can boost your sender reputation. Otherwise, if your emails are consistently deleted without being opened or they are marked as spam, that deteriorates your sender reputation and might result in your emails ending up in spam or junk folders more often.

Conclusively, both these technical and content related aspects are relevant to reaching the inbox and avoiding the spam folder.

If you are migrating and want to warmup your sender reputation, consider doing a welcome campaign which attracts positive interaction with your emails. For instance, start by sending out to smaller portions of your contact list and try to attract more opens and clicks with relevant and personalized content.

Extra: internal deliverability

Oftentimes when a subdomain setup as described above is implemented without whitelisting, internal firewalls or spam filters block mails or content in the internal organization (network). You might notice images not showing or mails ending up in the spam folder. Preapproving the subdomain by adding it to the internal whitelist usually solves this issue.

Source: many thanks to