Troubleshooting for Deliverability Problems

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About Deliverability Problems

Overview

If the sending of your emails does not run smoothly, we talk about deliverability problems. These can take the form of bounces or spam delivery, or be visible through poor email KPIs such as low open and click rates. This article explains these problems and measures for resolving them.

Bounces

Deliverability problems can occur in the form of hard bounces or soft bounces. In the case of bounces, your emails are rejected by the email provider and not delivered to the recipient at all.

Hard bounces occur when the e-mail addresses or domains are unreachable or permanently unavailable. Soft bounces, on the other hand, can be caused by various factors, from full mailboxes, temporarily unavailable mailboxes to reputation-based blocking by providers.

The exact reason for the bounce can often be deduced from the bounce message. The bounce rate is an important KPI to identify problems with email strategies. This is visible in Optimizely Campaign in the Campaign Analysis and the Performance Dashboard.

Spam delivery

In addition to bounces, spam delivery of your emails can also affect the success of your email campaign. Although the emails are accepted by the provider, they are not delivered to the recipient's inbox, but to the spam folder. Emails that end up in the spam folder are generally read significantly less and generate poor open and click rates.

However, the information as to whether and how many emails are delivered to the spam folder is a KPI that is not communicated by the email providers. It can only be determined by sending test emails to the various providers and by monitoring the open rates, which are much lower for emails presented as spam.

Causes of deliverability problems

There can be many reasons for deliverability problems. The most important ones for optimizing your strategy are related to your sender reputation, sending behavior and the contents of your emails. These reasons are explained in the following table.

Cause Explanation
Poor IP or domain reputation Mailbox providers collect various metrics on your mailings and assign a reputation to your sending IPs and domains based on this. If they assign negative points based on your sending behavior, your sender reputation will be downgraded. See also our Sender Reputation Guide.
Spam filtering Mailbox providers work with complex, self-learning spam filtering systems, which strike at content elements and compare your e-mail content with known spam e-mails and possibly block them.
Negative or low email KPIs Negative KPIs such as high bounce and complaint rates also have a negative impact on deliverability, as do low open rates that are below 10% over a longer period or fall regularly.
Spam trap hits and blocklistings Sending to spam traps can lead to blocklistings of your sending IPs or domains. Depending on the importance of the blocklist, such a listing can lead to a complete block of your emails with various providers.
Content suspected of being spam Certain content components or the lack of these can also trigger a spam filter to reject your emails, including a missing text version, phishing-suspicious links, spam trigger words and phrases, large amounts of money, text in bold, red font, or excessive use of images. For more information, see Email Content Best Practices.
Poor list quality The quality of a recipient list suffers above all from old data that is not removed, email addresses that were collected without DOI, a complicated unsubscribe process or a lack of list hygiene measures, for example by not excluding inactive contacts.
Problematic sending strategy If only the entire database is ever contacted without any segmentation, and possibly also under a too high frequency, this can also have a negative impact on deliverability performance.
Missing domain authentication Missing email authentication such as SPF, DKIM and DMARC can lead to deliverability problems. See also Email authentication and encryption.
List Bombing The misuse of unsecured registration forms by bots that enter masses of email addresses and trigger DOI emails often leads to high complaints and can result in further deliverability problems. Further information at List Bombing.

Troubleshooting Guidelines

Depending on the problem in question, different approaches are required to solve it. Our Campaign Support and Deliverability teams will be happy to assist you. Below you will find a collection of measures that can help you to overcome deliverability problems.

  • Make sure that you only write to contacts with a valid opt-in (DOI) or customer relationship. Exclude contacts collected in other ways, e.g. through list purchasing, from the sending of advertising mailings.
  • Exclude inactive contacts who have not shown any activity in the last 12 or maximum 24 months from your regular mailings. These contacts can be sent less frequent reactivation campaigns.
  • Try our Send Time Optimization feature to send your email to your recipients at the exact time they read their emails.
  • Contact each recipient in your database at least once every 6 months to keep your list clean in the long term. Recipients who have not received any emails for more than 12 months should be excluded.
  • Monitor your email KPIs, especially the open rate. This should be at least 10% at all times and for every mailbox provider. This can be reached out through stricter list hygiene measures.
  • Check factors that can lead to a high complaint rate, such as the chosen opt-in method, the sending frequency and the relevance of the email content. And then optimize these if necessary.
  • Secure your registration forms against bot attacks, e.g. by implementing captchas, honeypot fields or IP restrictions.
  • Use as much segmentation as possible. Segment your recipients based on activity, regions, interests, age groups or products purchased, for example.
  • Challenge the mailing frequency and reduce it if necessary to avoid bombarding your recipients with emails.
  • Ensure transparent mailing content including unsubscribe and data protection links and a complete legal notice. Also ensure a balanced HTML/text ratio (40/60), identical text versions and do not send the entire content in a large image file.
  • Carry out a content test of your mailing and remove section by section to identify any problematic parts. This could be the header, footer, subject line or even the sender domain, for example. The problematic element is always recognized and penalized by the provider and must therefore be removed or redesigned.
  • Avoid peaks in your mailing volume. If you do want to send significantly more during the season, a short warm-up phase should take place to slowly let the mailbox providers prepare for the higher volume.

If all these measures do not work, the only thing left to do is the following:

Pause sending for a period of time and start a new warm-up to build up a good reputation with the mailbox providers again. To do this, only send to a small number of your active recipients at the beginning and slowly increase the volume until you have reached your targeted volume again. For more information on this, see IP warming.