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Subhankar Kundu in Transactional Emails

Pro Tips To Troubleshoot Any Email Delivery Issue

Many people take delivering emails for granted. Until they find out that the all the emails that were delivered successfully have actually ended up in the spam folder. The only solution to resolve this is by performing troubleshooting which includes a lot of trial and error.

Aritic Mail ensures to help customers troubleshoot such problems day in and day out. Therefore, this guide will give you some tips that we have learned over the years about deliverability in five key areas. You can also check out a bonus section at the end of the article of resources and tools. I think this must help you with any delivery issues you face.


Email authentication from your domain is the first thing you should check while performing troubleshooting of email delivery.  SPF, DKIM, DMARC, and Return-Path (if applicable) are the four vital things you should have configured to help cover the authentication process. It helps you control the genesis of your emails by letting the internet know which ones to allow. These four will give the postmaster the vital tools that will help verify the authenticity of emails and give you better options on the action that postmasters should take in case the email is not from you. The ESP should make it a priority to provide easy setup and management of these protocols.

This guide gives brief information about each protocol and link to the primary guides concerning each topic.

Verify The Authentication Setup Of The Domain Using The Following Tools


SPF or Sender Policy Framework is used to let the world know the origin of the emails for your domain. To create an SPF policy for your domain, you can use DNS TXT record. Their source is added to an SPF record that exists for every email.


DKIM officially known as Domain Keys Identified Mail serves the purpose of signing the outgoing messages cryptographically. This prevents altering of messages while sending them. DKIM is set up a bit like SPF. You will have to add to your DNS a new TXT record for your domain. All sources of emails for your domain will require a public key that is unique for each of them. Typically, Aritic Mail will always manage the DKIM. They will generate the private key and give the public key for the DNS records to you.


Typically, the Return-Path of the emails you send is used to determine whether the email will pass the alignment of DMARC and SPF. For your email to pass SPF alignment, DMARC requires the Return-Path domain to match the “From” domain. You will have to add CNAME record to the DNS if you want to set up a custom Return-Path on the emails that are sent using email providers. There are also some spam filters and ISPs that like to see reports that the Return-Path of domains matches the “from” domain. This means that it is a safe practice to set the Return-Path on emails that are sent using third-party providers whenever necessary.


DMARC, known as Domain-based Message Authentication, Reporting, and Conformance and it uses SPF and DKIM to offer the emails of your domain the extra layer of protection they need. It also helps in generating reports from ISPs that will show you the origin of every email for your domain. DMARC addresses some weak spots that DKIM and SPF have.


The content included in a message is very crucial. There are some things to look out for should you face any delivery hitches.

  • Use Litmus Putsmail to send text messages while checking your messages
  • Use Litmus to carry out thorough message testing
  • Always include plain text option when you send HTML emails
  • Do not use shortened URLs, especially when they are from
  • Do not use many images

Always check if the HTML is written well and is compliant. Avoid using many images and also ensure that you create a plain-text version of every email.

Anytime you notice that emails originally delivered to the inbox are being directed to the spam folder know that it is time to do some tests. If there are some changes that you had recently implemented, undo the changes and resend the email. Check if they are delivered to the inbox or not. Other than any major changes to the content pay close attention to any links or newly updated attachments. All these elements that make up a message are some of the triggers as we have seen over the years. Do not use shortened URLs in the messages because you will enable spammers to carry out their purpose as they use redirects to achieve their goals as they can easily hide in links. If you have a single shortened URL spam filters, then it will quarantine the message. Here is an example of how a simple and small change can affect you in big ways. One of our clients got their messages labeled as spam content by Gmail because they added a phone number. To resolve this issue, we only removed the phone number, and everything was fine.

To make things easier run all new messages through Litmus and to detect any red flags that may lead to problems with ISPs and providers of email security. This will help you avoid the need to track down issues one by one when a problem arises and help the content to meet all current laid down practices.


The way people engage with your messages will greatly affect your deliverability. Typically, ISPs and security providers will build your domain’s profile over time. Therefore, the best way to ensure an excellent engagement is by sending emails that are useful for the recipients. Emails that they require and expect too. Using DKIM will also help in building a reputation, and it will involve factors such as open rate, rate of bounce, and rate of spam.

  • Refrain from sending emails to addresses that bounce.
  • Never send from a “no reply” email address.
  • Always keep watch over the rates of bounces, spam, and open rates.

Hardly ever will a modern spam filter depend on keyword filtering. They tend to favor adaptive filters to protect users from different kinds of threats. For different providers, this is different, but user actions are incorporated into Gmail. Emails are handled differently for different recipients based on different things. This can include marking your messages as spam messages, ignoring them repeatedly, or marking the message as not spam message. Whenever you notice that there is the low engagement for transactional email by your recipients, audit the messages you send to the customers or users.  When you send too many emails in a short span, engagement level goes down. This will damage the reputation with time.

Good Signals

  • When the user opens your email, it shows engagement.
  • If a user replies, it shows conversation.
  • When a user marks as ‘not spam’, it shows that the ISP got it wrong.
  • If the user moves to a folder, it shows value for the content.
  • When a user adds to address book, it shows the sender’s value.

Bad Signal

  • When a user deletes it without opening, it shows their lack of interest. However, it is not the same as ‘mark as spam.’
  • If a user marks the email as spam.

Clicks are engaging factors that the ISPs fail to track. They see this as a breach of privacy, and therefore self-policing is the best practice. Typically, ESPs, through redirects, will report click data. Even so, ISPs have shared that this does not affect deliverability in any way.

Other than these signals closely monitor the rate of bounces. Ensure to keep bounces lower than 5% for the entire domain. Anything that is higher than this will speak against your deliverability reputation because ISPs will interpret that you are sending email to recipients who are not qualified. Therefore, mitigate this by removing emails that keep bouncing consistently.

An excellent transactional email should have no spam complaints. Ensure that your spam rate for the transactional email is at least 0.1%. While it may seem too ambitious to focus on having one spam complaint out of every 1,000 emails sent, it can be possible if your transactional emails are of high quality.

Aritic Mail will take care of your bounce rates and spam rate by deactivating any recipients after receiving complaints of hard bounces and spam complaints. To an extent, emails with regular soft bounces may also get their email addresses deactivated.

ESPs handle the list hygiene. Having a clean contact list across the domain is imperative. Other than deactivating recipients after hard bounces and spam complaints, avoid sending emails to a purchased contact list. If people only use your application once, don’t send welcome emails to them. Also, do not add their addresses to an email list without their consent.


Normally, you should look into two aspects that are involved in managing the reputation of your deliverability. IP reputation was used to check the original reputation. ISPs will monitor the traffic generated from IP addresses, and this translates to checking out for bulk and spam messages.

Since we are talking about IP reputation, we might as well look at the common myth that surrounds it. The myth claims that a dedicated IP address is a dependable way to address issues about deliverability. From the research, we learned that a remarkably managed pool of shared IP addresses would be more reliable. ESPs use dedicated addresses to lower the costs of support since they will not be monitoring traffic too closely. Through this, they can get some extra revenue from clients.

Real-time Blockhole Lists (RBLs) which are third-party resources will report any suspicious activity from an IP address to ISPs and postmasters.

ISPs incorporate the Domain reputation as a part of their testing methods in the recent years, and they depend mostly on it. This has resulted in need of RBLs to supplement their lists of IP addresses with domain’s activities list. For larger services such as Gmail, enough traffic data is collected to create proprietary lists of a reputation for IP and domain. Using the authentication standards on your domain, you can build a reputation that will be portable for all ESPs.

The downside to this is when your reputation is negative. When you use this approach, the negative reputation will follow you to any ESP you choose to use.  Recently, we helped a client resolve a problem causing their emails to go to spam in Gmail. Looking at Gmail Postmaster Tools, we realized that the problem was that the reputation was very poor due to the marketing emails at a different ISP. Sending transactional emails from similar domain still caused them to fall into spam category. It is up to you to manage your domain’s good practices just as it for ESP’s reputation to be managed by them.


You should always be concerned about infrastructure if you run your email stack. This includes the reputation of the IP, feedback loops, reverse DNS, and a few low-end protocols. Luckily, a good ESP will take care of this for you.

Email provider will monitor the IP address reputation. It is used to determine the email that is either marked as spam or discarded. IP reputation is slowly decreasing in its value because of domain reputation tools. Even so, it is important for deliverability. Using your web host to send an IP can still pose some problems since these shared IP addresses from AWS and VPS can have a reputation that is not good.

Mail Providers, through Feedback loops, have found a dedicated way to report to ESPs about any activity regarding spam. For any configured feedback loop, each IP address information will be included and an email address that parses inbound reports to check for actionable data.  Word to the Wise will always keep an updated page with ISP information and have a place to sign up for feedback loops relating to different ISPs.

Reverse DNS or rDNS verifies IP addresses associated with a certain domain. Spammers tactics have changed such that they make rDNS an ineffective way for spam quarantine. It has done so by avoiding the use of botnets to send their campaigns. Even so, it is crucial to have this rightly configured.

Ensure that you use a mail transfer agent (MTS) that will support DKIM. Some great choices to look at include Postfix and PowerMTA.

Get It All In The Inbox

Email deliverability has no silver bullet. ISPs and email security providers cannot offer precise guidelines and ensure emails get into inbox. Because they are always playing cat and mouse games with spammers. If you follow these steps and you will improve the chances of your emails delivered to the inboxes.

Resource And Tools

AOL Postmaster -Combination of tools and articles to use for sending to those using AOL – DKIM project’s official home – DMARC project’s official home

Gmail Postmaster Tools – Analysis and tools to use for sending to those using Gmail

Litmus – A suite of tools you can use to test the design and probability of spam

Litmus Putsmail – Free Litmus tool used to test HTML emails before they are sent

Mail-Tester – A free tool used to check your email’s spamminess

MX Toolbox– Tool for checking blacklists and DNS records as well as other resources related to emails postmaster tools  – Offers information concerning sending to as well as tips for solving problems

Port 25 authentication email verification – An email report that will check SPF, the SenderID, the DomainKeys, DKIM, and SpamAssassin

Word to the Wise ISP information – Checks for sending limits of an ISP and other information about deliverability

Yahoo Postmaster – Tools and articles for sending to people who use Yahoo

250ok Postmaster Tools – Used for testing DNS, Gmail placement of Tab, and others


1 Comment

Prateek Dash

Sending an eCommerce transactional email is complicated. No one likes to send an email that bounces or ends up in the SPAM folder.

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