Best Practices for Deliverability

Now more than ever reaching the inbox is going to be critical to your holiday revenue. As always during this time, the ISPs filtering can become more strict while at the same time senders are changing audience, list size and cadence. We have some guidance on how you can mitigate the risk of a deliverability issue with all of those factors in play.

Maintain Sender Reputation During the Holidays

As the holidays approach, senders are ramping up their marketing programs and their send volume – in 2021 as we continue to see, holiday ramp up will be over a longer timeframe with higher volume early on in the pre holiday season. With this influx in volume, the ISPs must make adjustments to how they accept and deliver mail. All senders are competing for more limited inbox placement, so ensuring your sender reputation is, and remains healthy will be critical to reaching your recipients.  

If you plan on doing anything out of the norm this holiday season, including the following: adjusting suppressions/smart lists to send to a wider audience and/or increased send volume due to sending additional campaigns, please reach out to your CSM or Support. Sailthru can help to provide strategy on how to reach different audiences in a way that mitigates deliverability risk.

What metrics are the ISPs looking at when scoring your sender reputation?

  • User Engagement
  • Invalid Addresses (Hard Bounces)
  • User Complaints
  • Spam Trap Hits
  • Drastic Changes in Send Volume 

What should I monitor to be sure we are not having a deliverability issue (inbox or blocking?)

  • Monitor Open Rates by top domains using the Domains tab in Campaign Summary. Open rates should be consistent across the top ISPs, if one is significantly lower than the rest, you may have an inboxing issue at that top domain.
  • Gmail Postmaster Tool. If your IP and/or Domain Reputation dips below Medium to Low or Bad, that is usually an indicator of a Sender Reputation issue at Gmail resulting in mail being filtered to the spam folder.
  • Soft Bounce Rates. If Soft Bounces are are higher than the norm across any major ISPs, reach out to Sailthru as this is likely the ISPs blocking your mail due to abusive metrics/poor sender reputation

What should I monitor to be sure I am not at risk for a deliverability issue?

  • Hard Bounce Rates. If Hard Bounces are above 0.5% check the audience in which you sent to.
  • Complaint Rates. High complaint rates indicate that users do not like what you are sending – either the content or frequency. Monitor complaint rates with each send.
  • Review overall open rates for changes to your norm. Low open rates can show poorer engagement and play an important role in your reputation.
  • Review opt-out rates. You don’t want to sacrifice your loyal year-round list for the holiday season. If opt-out rates rise, take a look at what you are doing and adjust.
  • Increase in sign ups that are potential BOTs and not valid users. While BOTs can hit sign up pages with email addresses across all ISPs, we tend to see BOTs hit with Chinese or Russian domains (,,, etc.) Any major spike in sign ups out of the norm should be investigated immediately.
    • Proactively implement Google reCAPTCHA to eliminate the risk of a BOT attack.

Please note most holiday strategies involve sending to less engaged users and/or users at a more regular cadence then normal which tend to result in spikes in Hard Bounces and Complaints, and decreases in User Engagement. So it is very important to be closely monitoring these metrics and ensuring if they do change from your norm, that your delivery and inboxing are not being impacted.

Helpful Recommendations:

  • Do not introduce any new lists that are not currently being mailed to via Sailthru.
  • Do not mail to older lists that have not been consistently mailed to.
  • Do not fully remove suppression lists. If you want to begin sending to lesser engaged users slowly begin pushing this back well before the holiday season starts. That way if we do see issues we can work to mitigate them prior to the holiday season.
  • Be cautious of new acquisition sources. Test them prior to holiday season and be sure they are not resulting in poor quality metrics (Hard Bounces and Complaints)
  • Be careful editing your sign up and opt out pages.
  • Be careful changing your sending cadence. ISPs will penalize you for an inconsistent spike in send volume, so increases in cadence should happen slowly. Provide preferences to allow users to opt down from increased marketing.
  • Do not change your sending domain.

As always, our Deliverability and Customer Success teams are here to help with your holiday strategies and plans. Please reach out with any questions or if you plan on doing anything listed as what not to do above.

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