Emails going to the spam folder instead of the inbox is a constant struggle for ecommerce email marketing. However, deliverability to inbox vs spam box is not an easy black-and-white issue with simple answers. Every email service provider is different and each applies different spam filtering criteria. On top of that, email providers never disclose the reasons for blocking or spam-foldering emails, as this would just give spammers a checklist for how to avoid the filter.
Here are some tips and resources that you can reference for your own evaluation and future sends:
1. Work to maximize engagement - Email providers monitor opens and clicks, and higher rates of engagement will help your emails avoid the spam box. Using carefully targeted emails (taking advantage of Cortex and Smart Segments) will improve engagement over traditional email blasts. Make sure that disengaged users are removed at regular intervals – users who don't open messages tell mailbox providers "this message isn't important", and this affects sender reputation and inbox negatively.
2. Avoid large jumps in send volume - Email providers watch the volume of email that comes from each sender, and sudden increases in volume run a higher risk of being marked as spam. Using targeted emails at a steady volume (handled automatically with Cortex) is the safest tactic to avoid volume related flags and large amounts of unsubscribes. Consistency in send volume the key here.
3. Make unsubscribing easy - No one wants unsubscribes, but spam reports are far worse. If you make it difficult to unsubscribe from emails users become much more likely to click the "mark as spam" button to block your emails. Any users who mark your emails as spam are automatically unsubscribed in the ReSci system.
4. Ask your subscribers to whitelist you - Getting users to add you to their address books, or labeling your emails with "never send to spam" improves your reputation with those email providers.
5. Avoid "spam words" - Common "spam words" or phrases in your subject line and email content make your email much more likely to be flagged as spam. "For free" "Risk free" "Buy/Try it now" "Save big" and "Only (price)" are some phrases commonly found in both legitimate e-commerce sends and spam emails. Additionally, avoid repeating your subject line in the content of your email. Check out Comm100's spam word guide here.
6. Avoid overly embellished text - Fonts that are too large (over 16px), bright colors (especially red), or overly styled (like with "highlighter" effects) can trigger spam filters. Overuse of exclamation points, ellipses, and other punctuation can also cause your emails to be flagged.
7. Avoid emails that are only images - Many spammers use images containing text to avoid triggering spam phrase filters, so email providers have begun filtering emails that do not have enough text to evaluate the content. Header, banner, menu, and Call To Action images are great, but adding more text to your emails can potentially improve your inboxing.
8. Include plain text options with your html email - Including plain text content and alt text with images gives spam filters more information to look at and shows you care about giving your subscribers a choice in how they view your email. Including alt text is very easy, while coding an alternate plain text template inside your existing html is much more complex. Learn more about alt text here, and coding plain text options into your html here.
Even if you do all of these things and do them perfectly, your emails may still end up in the junk folder. Email spam filters' criteria change almost daily and can be impacted by things that you have no control over. However, if you, as a habit, send good emails that your customers want and interact with, you'll get into the inbox more often than not.
Email delivery articles and resources here to help with your inboxing and deliverability.
Hopefully this information gives you some additional insight into the factors that go into inbox/spam sorting on the client side. You can always split your sends with A/B testing segments if you want to test different template styles, subject lines, send schedules, and coding practices with regard to inboxing and deliverability.