What is Email Deliverability?

Simply put, successful email deliverability is your message arriving in the inbox of the recipient as intended. Email deliverability failure is when your message is either routed to the junk/bulk folder or blocked by an ISP (Internet Service Provider).

So, how do you make sure your email gets delivered? Luckily there are proven techniques to prevent failures and improve your email delivery rates for the long-term. This guide offers an overview of the steps most businesses need to take to maximize their email deliverability. Learn about:
Reputation ›
Infrastructure ›
Authentication ›
Top 5 Email Deliverability Best Practices ›



The first step in helping ensure email deliverability is reputation. In the world of email, sending reputation refers to a set of specific metrics directly related to your email sending practices. Senders with good reputations get delivered. Senders with poor reputations get blocked at the gateway or their messages land in the “junk” folder instead of the inbox.


A strong sending reputation, like a great brand or personal reputation, is built over time. Here are the metrics ISPs look for when determining sending reputation:


Sending quality email that your subscribers want to receive is the basis of a great sending (and brand) reputation. Ensure that your recipients want to receive your email by implementing a clear opt-in during the subscription process and be sure to send relevant and interesting content. Also, make sure your HTML is properly formatted—poorly coded emails get caught in filters or don’t render properly.


How much email do you send? High-volume senders are always a red flag, especially when volumes are inconsistent. Do you send approximately the same number of emails each week or month, or is your sending schedule all over the map? Consistent volumes based on subscriber preferences are a key consideration for ISPs.


Do your subscribers complain or tag your messages as “junk” or “spam”? Even a tiny increase in complaints can cause your email to be blocked by the ISPs. Keeping your complaint rate very low (less than .1% of email that is sent and accepted by the ISP) is very important.


Sending to even one spam trap or “honey pot” will instantly set back your reputation and cause deliverability problems. When you send to a spam trap (an email address activated by an ISP to catch spammers), it means you’re engaging in email address harvesting (an illegal practice) or your list hygiene practices are weak. Either way, ISPs aren’t going to deliver your email.


A good reputation also means that only a small percentage of your emails “bounce” back or are returned by the ISPs because the account is no longer active (hard bounce) or the mailbox is temporarily full or the recipient is out-of-office (soft bounce). If a lot of your mail is bouncing back, it means your subscribers aren’t engaged and you’re not keeping up to date with them. It also indicates that your list hygiene practices are not up to industry standards. This makes your email look like spam to an ISP and your email is unlikely to get delivered. Keeping your bounce rate low by implementing procedures to immediately remove email addresses that return “hard” bounces is essential.


Appearing on just one of the leading blacklists is enough to get you blocked by some ISPs. Senders with low complaints, who don’t hit spam traps, and who send email consistently generally don’t get blacklisted. However, if you do get blacklisted, having a good sending reputation will help convince the blacklist administrator to remove your IPs from their list.



Setting up and maintaining infrastructure for high-volume email is complex, challenging, and expensive. It’s not as simple as maintaining a corporate email environment, and very different rules and standards apply. You’ll either need dedicated staff who understand the ins and outs of email to monitor your email program,

Using Dedicated IP address.

XtreemPMTA create a secure server configuration based on Linux operating system that we’ll be able to access it over SSHand SFTP. We’ll have webmail, POP3, IMAP and SMTP for our system emails like postmaster, abuse, DMARC, … We’ll setup reverse DNSmultiple IPs, domains, … and at the end automatic backups so our work will not be lost in case anything goes wrong.

Your Bulk Email server will use PowerMTA with a smart queue and custom domain rules for best deliverability. PowerMTA will also take care of automatic bounce processingunlimited SMTPs/MTAs and backoff rules so that even the worst case scenarios will have a happy ending. Of course, we’ll also make sure our DKIM, DMARC and SPF records are setup correctly and that Feedback loops (FBL) or spam complaints are properly taken care of without any work from our end.



Domain reputation identifies legitimate senders based on their domain name rather than their IP address by using the DKIM authentication protocol. There has been a sharp move towards domain reputation predicated by the move from IPV4 networks to IPV6 networks. While it’s not yet common practice to use domain reputation required under IPV6 (though Gmail is already the strongest proponent), the ISPs are starting to use the combination of IP and domain reputation until IPV6 is fully adopted.

The key benefit to domain reputation is reputation portability that enables ISPs to track sender reputation regardless of IP and frees senders to move between email service providers. Domain reputation will also help senders who move to a new IP to not have to warm up. The theory is (and keep in mind this is a theory), if you have a domain that has a good reputation, when you move to a new IP address, recipient ISPs will not require senders to warm up their IP because they will already know what volume to expect due to your domain’s reputation.

This also means if you tarnish your domain reputation, it makes it much more difficult to start from scratch with a new domain.

Bottom line: Senders should focus on both domain and IP reputation in order to maximize email deliverability.





Once your email program is up and running, you need to make sure you keep your reputation intact and your recipients happy. This section covers the best ways to ensure your email campaigns stay on track, including preference center ideas and tips for sending the best content possible.


1. Ask Permission, Host a Preference Center

Watch out for email fatigue. Sending too much email to your users can drive high unsubscribe and/or complaint rates. Offer a preference center so users can choose what updates they’d like to receive and how often they would like to receive them.

2. Keep a Clean List, Avoid Traps

A clean, well-managed subscriber list can be your best asset, whereas “dirty” lists with out-of-date information are a leading cause of deliverability failures and are sure to damage your sending reputation. List hygiene is the process of removing “bad” addresses in a timely manner. Good list hygiene practices are essential to avoiding spam traps and keeping your bounce rates low—key drivers of your reputation. There is no better way to ensure consistent deliverability success than by regularly cleaning your list of hard bounces, unknown users, and other inactive addresses. SendGrid’s real-time Event Webhook is a great start, providing instant information like opens, bounces, and unsubscribe requests for individual subscriber records.

3. Send a Welcome Message

Welcome messages are the cornerstone of a well-run email program. When was the last time you signed up for a new online service and didn’t receive an immediate message confirming the sign up? Welcome messages (like other transactional emails) are more than confirmations, they’re an opportunity to engage with subscribers and to start the relationship off on the right foot.

4. Follow the Law

Be sure to comply with the federal CAN-SPAM Act. The CAN-SPAM Act is geared towards marketing email (with transactional email technically being exempt), but we advise that senders follow its regulations regardless of what type of email they send.

5. Send Good Email

It sounds obvious, but it’s actually harder than it sounds. There is no secret formula to sending email that works. First, make sure you’re following the four suggestions outlined above. Second, the content of your emails needs to be relevant, interesting, and aesthetically aligned with your

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