In this article, you'll learn many of the actions you can take when troubleshooting the deliverability of your mailings, including:
Deliverability issues - bounced messages
If you are maintaining a good sender reputation, following list best practices, and using a dedicated sending IP, you are less likely to experience deliverability issues. However, you may come across some bounces and blocks, so ruling out major pitfalls may help get to a solution.
With that said, it is important to remember that mail receivers and spam filters are protecting their users from spam and do not fully disclose their filtering rules (each system has a different set of rules), so sometimes it can be difficult to get to a specific resolution.
To assist you in troubleshooting a deliverability issue, you can follow the steps below to rule out some of the major causes:
Step 1 - Check DKIM authentication on sending domain(s)
Use one of the two methods below:
- Navigate to Admin > Setup > Email Authentication and follow the steps in the Email Authentication section of the Sender Authentication page to test.
- Using this template, create an email address based on an email account you currently own. For example, to send the results to: firstname.lastname@example.org the sample message should be sent to "email@example.com" You would then create a mailing in Communications Professional (or use an existing one) and publish the email to your unique address that you created. You will receive the authentication results to your email account (example below of SPF and DKIM passing)
Summary of Results
- SPF check: pass
- "iprev" check: pass
- DKIM check: pass
- SpamAssassin check: ham (NOTE: this can be ignored for the authentication tests)
If the DKIM check is neutral or failing, then it is recommended DKIM authentication is completed before continuing to the next step.
NOTE: Refer to the Email Authentication section of the Sender Authentication page for more information.
Step 2 - Check the setup and content of the mailing
- Make sure the “from” address used for the mailing has been authenticated with DKIM.
- If there was a large spike or dip in volume, some mail receivers will classify the message as spam.
- Check to see if there are any exposed URLs in the body of the mailing (e.g., www.website.com). If so, cover them with text or an image to avoid being misconstrued as a phishing attempt.
- Does the mailing contain any third party or short links? (e.g., bit.ly, sbn29.com) If so, consider using an alternative because short links are typically blocklisted and may cause your emails to be blocked or classified as spam.
- Are any URLs used in your mailing on a known blocklist? Check your URL's reputation.
- If using images in the body of your mailing, make sure you have enough text to go along with it in order to create a good balance. Using only images with no text can look suspicious because spammers have been known to hide text and other malicious content embedded in an image.
Step 3 - Look at the sent mailing results
- Check to see if you received any subscriber complaints or unsubscribers in the Key Metrics tab of the sent mailing (Mailings > View > Sent). This is a key component in determining your sender reputation and how your mail is being classified.
- Look at unsubscribe reasons to help understand some important deliverability questions (do individuals consider your messages spam, are you sending too frequently, are you sending to the wrong audience).
- Select one of the bounce types in your mailing (soft, hard, or blocked) in order to get to more detailed info.
- Select a recipient from the list and navigate to the Mailings tab. Then, select the Blocked or Bounce link to view the detailed error message.
- Look for the Diagnostic-Code within the blocked or bounce message details. Sometimes, you will be able to see what may have caused the bounce to occur (spam content, ISP or spam filter block, poor sender reputation, blocklisting).
- You can see if a block is affecting specific domains if you navigate to the Details tab > Non Delivered > Domain Blocks.
- If the block is concerning a small, private domain, contact the "postmaster" of the domain and request that your IP address and/or sending domain be add to an allowlist.
- If the block is concerning a major ISP, such as AOL or Comcast, you may want to submit a ticket to request the block be lifted. You can also create a case for additional deliverability assistance.
To sum up...
- Only send from domains that are authenticated through Communications Professional
- Only send messages to individuals who have opted in (our rules of use)
- Keep mailing lists updated and follow best list practices
- Many email providers look at user engagement when classifying mail
- Keep your sending volume consistent
- Check the content and subject line for deliverability best practices (check using MailTester)
- Maintain a good sender reputation
Bounce types overview
A bounce occurs when a mailing cannot be delivered to a particular email address. There are several bounce classifications: soft bounces, hard bounces, and blocks. Ultimately, if you are experiencing multiple bounces, you may need to clean your subscriber lists and target groups to improve your deliverability.
Let’s take a look at the key reasons you might experience each bounce type.
A soft bounce generally occurs for one of the following reasons:
- The mail server was down
- The mail server was not accepting mail
- The subscriber’s inbox was full
You can generally resend a mailing to subscribers that soft bounced at a different time to ensure that they receive your message. Soft bouncers are automatically re-tried (i.e., re-sent a mailing) at certain intervals based on domain.
A hard bounce generally occurs because:
- The domain does not exist
- The domain does not have a mail server
- The email address does not exist in the domain
These addresses cannot receive a message because there is no place/address to receive the mailing.
A blocked email address is any email address that may remain deliverable, but is rejected by the receiving mail server (e.g., an anti-spam filter rejects your mailing).
When a specific email address bounces multiple times, email addresses become known as repeat bouncers. These can be determined by soft, hard bounces, and blocked (Refer to Rules below). Repeat bouncers are automatically unsubscribed.
Because bouncing can cause deliverability problems, Communications Professional uses the following rules to evaluate bounce status and suppress the email address when it reaches the repeat bouncer status. Note that these rules draw on data from the past 90 days of mailing activity.
- After three consecutive hard bounces, a subscriber’s delivery format is automatically switched to Text.
- After four consecutive hard bounces, a subscriber becomes a repeat bouncer.
- After six consecutive bounces (a combination of soft, hard, or blocked), a subscriber’s delivery format is automatically switched to Text.
- After seven consecutive bounces (a combination of soft, hard, or blocked), a subscriber becomes a repeat bouncer.
- After one hard bounce, an AOL email address becomes a repeat bouncer.
- Admin, Login, and Test email addresses do not become repeat bouncers.
What to do when a mailing is not being received
There are many reasons that can keep a mailing from being received. If you or a subscriber are having issues receiving test or sent mailings through Communications Professional, you can follow the steps below to help determine the problem.
- Search for the subscriber record in Communications Professional to see if the mailing was delivered by navigating to Subscribers > Search > Details & History > Mailings. If the mailing is shown as being delivered, then the issue lies with the receiver's filter settings. If the mail is showing a bounce or block, refer to the Troubleshooting Deliverability Issues - Bounced Messages section above to troubleshoot further.
- It may be necessary to look up all recipients with that domain to see if just one or all are not receiving the mail.
- If it is only one recipient, then it is likely a user setting (ask them to add you to their address book or have them check their spam or junk folder for the mailing and move to the inbox). Refer to the User Inbox Preferences section of the Best Practices page for more information.
- If the issue is happening with all of the recipients, then there is a global issue with receiving the mail and you may need to reach out to that domain owner or postmaster (if it's a private domain) to have your IPs/domain added to an allowlist. Refer to the Allowlist section below for more information.
- Check the content of your mailing; content plays a big role in whether or not mail is classified as spam. Test the content using our Virtual Inbox test or by sending an email to MailTester and checking the results. You can also check out additional tips here to avoid being classified as spam.
- If you haven't checked your sender authentication (which is similar to a license to send email), follow Step 1 in the Troubleshooting Deliverability Issues - Bounced Messages section above. This is another factor that affects your deliverability, so it is important to have this in place (and to rule this out as a potential cause).
How to manually resend a soft bounce
While Communications Professional will automatically resend a message that resulted in a soft bounce, you may need to manually resend messages that soft bounce if the receiving system is down for a significant amount of time. Let's take a look at how to accomplish this in case this scenario ever happens to you.
- Navigate to Mailings > View (or Mailing Designer 2.0 > View if that's the feature you're using).
- On the Sent tab, hover over a message's menu and select Report.
- In the Non-Delivered > Soft Bounce section, click the numbered hyperlink.
- Check the boxes to select one or more messages, and then click Resend.
Blocklist, allowlist, and greylist
It's important to understand blocklists and their impact on your deliverability. There are three important list types that you'll want to understand in relation to blocklists:
Let's take a look at the different definitions, and what you can do to avoid blocklists.
A blocklist contains IP addresses and domains that are suspected of sending spam. Many email servers and spam filters filter mail based on whether the sender's IP is on a blocklist. Ultimately, blocklists help to filter out spam and protect the recipients.
A greylist contains the IP addresses and domains of bulk senders. Greylisting can be used by receiving mail servers to temporarily reject mail coming from bulk senders. They can be used to deter spammers because most legitimate senders attempt to retry the mail that is rejected while many spammers do not. Communications Professional automatically retries temporary errors to deliver mailings.
An allowlist contains IP addresses, domains, and email addresses considered safe senders at the mail receiver or spam filter levels. This can help identify legitimate mail to be received without being labeled as "spam" or "junk." Allowlisting does not always prevent mail from being classified as spam; if mail is sent with patterns that are characteristic of spam, it is very likely the mail will be filtered.
To learn more about allowlisting, see IP Address Allowlist (Communications Professional).
How does a sender become blocklisted?
A sender is typically blocklisted due to sending mail to spam trap addresses, receiving complaints, spikes/dips in sending volume, and sending spam-related content.
How does a sender avoid being blocklisted?
Unfortunately, getting blocklisted is common and often unavoidable. However, there are some things you can do to reduce the likelihood of being blocklisted.
- Send only to engaged, opted-in subscribers
- Send at a consistent volume
- Include a clear unsubscribe mechanism on all mailings
- Avoid common spam triggers (avoid third-party link shorteners, spam trigger words, image mapping)
What do I do if I'm blocklisted?
Many blocklists are temporary and auto-delist. However, some lists require remediation, which Communications Professional monitors. Remember, it is up to the email marketer to follow sender best practices and maintain a good sender reputation!