Best practices for email delivery

Microsoft Corporation

Aug, 2014


This whitepaper helps you identity the critical factors that affect the deliverability of your email messages and highlights good practices to help you choose a secure and reliable sending infrastructure, professional deliverability support, and good content for your recipients to help build your sender reputation.

Applies To

Microsoft Dynamics Marketing Spring ‘14 and higher


Email deliverability, usually expressed as a percentage, measures how many emails actually make it into the inbox. Email deliverability includes anything that is involved with the delivery of your emails, from the sending tools to all the intermediate steps (ISPs, MTAs, etc.). Proactive deliverability management ensures successful email marketing while complying with the business rules that govern email. When sending a high volume of emails the way those emails are delivered is crucial in terms of how they will be interpreted by ISPs and anti-spam filters. For instance, emails can end up in a recipient’s junk folder or they can be blocked by an ISP (without any warning or notification). Sometimes the email bounce metric reflects only a small proportion of all the emails that don’t get delivered.

Terms definitions

Term Definitions


Blacklisting services constantly monitor the Internet for spammers. When a sender IP address is blacklisted (that is, it has been identified as spam) the email sent from that address may not be delivered.


An Email Service Provider is an organization providing email services, usually focusing on email marketing.

Feedback Loop

These are feedback processes spanning different organizations where mailbox providers forward their customers’ complaints to the senders’ organizations, often ESPs. See here for more details.


An Internet Service Provider is an organization providing services for accessing or using the Internet.

Spam trap

These are email addresses created and maintained by ISPs and third-party blacklisting companies with the sole purpose of detecting spam senders. Using such addresses in a mailing can harm your reputation and land you on a list that identifies you as a sender of spam messages. That alone is a good reason to avoid purchasing or renting marketing lists.

Your sending reputation counts

Reputation is a metric used by ISPs to distinguish legitimate email marketing senders from spammers and other malicious senders. Simply put, if you send relevant emails to willing recipients your sending reputation will increase over time. If you deviate from this pattern (for example having inconsistent volumes, uninteresting content for your recipients, and so on) your reputation will be hurt.

ISPs keep track of senders’ reputations in various ways. The emails sent by those with low reputation can be blocked right away or they end up in the recipients’ spam folders. A good sending reputation is critical in ensuring high deliverability rates, but it is built over time. Using a reliable email sending infrastructure and service provider will make it easier to build a good sending reputation as we will see in the rest of this document.

Infrastructure aspects impacting deliverability

Having a professionally configured and maintained infrastructure is essential in ensuring high deliverability rates. Apart from problems like blocking or filtering there are a few other considerations that can tremendously affect deliverability.

IP addresses

An important decision is whether to request exclusively dedicated IP addresses from your Email Service Provider or to use the standard shared IP pools. It is a common misconception that shared IP addresses are problematic. If your Email Service Provider routes emails according to your reputation and volumes, shared IP addresses can be beneficial. Shared sending IP addresses cushion you from uneven sending volumes and occasional missteps in deliverability because the IP addresses are shared with other virtuous senders that will help sustain a steady reputation. On the other hand, if you are an expert in email marketing and plan to reach steady daily sending volumes over time, then dedicated IP addresses can be more advantageous. In that case you can split volumes between IP addresses used for transactional emails and those used for marketing or promotional emails.

Secure infrastructure

It is important to rely on a secure infrastructure by following the best practices of network and physical security to avoid access by unexpected users.

Feedback loops

Sign up for ISP Feedback Loops with all the major ISPs and act on complaints quickly and effectively. Also have “postmaster” and “abuse” mailboxes set up for all your domains and monitor them frequently. These mailboxes are also used by ISPs that don’t have Feedback Loops and by recipients looking to file direct complaints.

Make sure your sending domain is able to receive emails and has valid DNS record types like MX, A, PTR, and TXT records (see the complete list of DNS record types). If not, some ISPs will block emails from your domain.


Authentication is a process to validate that your emails are actually from you (and not somebody else impersonating you). It applies to both transactional and promotional emails. Authenticating your emails does not ensure your email will be delivered, but it helps ISPs to differentiate you from spammers and other illegitimate senders.

There are two accepted methods of authentication that you should implement: Sender Policy Framework (SPF) and Domain Keys Identified Mail (DKIM).

Your contribution to your email deliverability rates

Relying on a good service provider and email sending infrastructure that provides what we discussed before makes your work much easier but it is still not a guarantee of high deliverability rates per se. Service providers will look for suppressing known spam-traps and bad email addresses, among the other things, but cannot guarantee high deliverability rates. You are ultimately responsible for the content you send and to whom you send it. This section describes what you should do to maximize your email deliverability rates.

Keep your marketing lists clean and up-to-date

Attempting to send to outdated email addresses in marketing lists is a common cause of sending reputation damage. The process of keeping marketing lists up-to-date is called “list hygiene” and it is essential to keep bounce rates low and avoid spam traps.

Services like Microsoft Dynamics Marketing ensure automatic handling of hard bounces. Even with this support, periodic cleanup of marketing lists is always beneficial. Consider engaging with these recipients to obtain an updated email address or to have them subscribe again, in case of unsubscribed users.

Avoid acquiring third-party marketing lists. While the promise of instant marketing databases is alluring, employing such lists is a recipe for disaster in terms of deliverability.

A good way to ensure you have a high quality marketing list is to have a double opt-in mechanism in place where users will need to verify the subscription to your list via opening a link in a confirmation email sent to the email address they indicated.

Make sure you are compliant with the law

If you are new to email marketing, before reaching out to recipients in a country/region you should study the local laws regarding email marketing communications. It is important to be familiar with the details of these laws in all the countries/regions you plan to reach, and design your communication accordingly. For instance, in order to comply with the US Federal CAN-SPAM law you will need to comply with a number of requirements, among them:

  • Provide a working unsubscribe mechanism clearly accessible in all email communications. It is critical that if a recipient wishes to remove himself from the communication he can do so in a few clicks. Also a link to the subscription center is a useful addition.

  • Include your official business street address in all email communications. This cannot be a PO Box and it should be your corporate headquarters or another address where official communications are handled.

  • Handle all unsubscribe requests immediately or at least within 10 business days.

Other laws like Canada's anti-spam legislation (CASL), Australia’s Spam Act or the various European equivalents can be seen as extensions on these principles, usually being stricter in requiring preliminary recipient consent, before being eligible for promotional communication.

Provide your recipients a direct way to unsubscribe without marking your email as spam. Apart from complying with the legal requirements, providing a link to a subscription center in all your promotional emails will also improve your overall sending reputation as a genuine company.

Monitor your results and complaints

You should constantly monitor the results you get from your sent emails and reply promptly to any request from your email deliverability service desk. The latter is critical. If you don’t act immediately at the request of your email deliverability service desk you might be quickly excluded from sending emails.

Monitoring the results of your emails is also important to finding deliverability patterns and acting upon them. Some ISPs treat some aspects of an email differently so monitoring the results across various ISPs can give you insights on what to tweak. For example, an unusual high number of soft bounces might be caused by deliverability issues.

Provide a plain version of your email

Make sure you always provide a plain text version of your email along with the main content that matches closely the HTML version. This will increase your deliverability rates and provides an easy-to-read format for recipients using text-based email software. Keep in mind that in many cases this text version will be read on mobile phones, so structure the content accordingly (shorter text, clearly separated paragraphs etc.).

Provide meaningful values for Subject, From, and Reply-to fields

Make sure you provide a meaningful subject line for your email. Refrain from all caps text, too many exclamation points and duplicate content. Identify your communication clearly as advertisement if that is the case and avoid placing misleading subject lines. This requirement might be critical due to legal reasons in some jurisdictions. Similarly, having a meaningful and consistent “From” address is also important. Don’t use “no-reply” or similar addresses in the “From” field. Keep in mind that receiving an email from an impersonal, unknown sender might raise the chances that your recipients will mark your email as spam and might be non-compliant with anti-spam laws in some countries/regions.

Add content that is relevant to your recipients

Create your email content so that it is relevant to your recipients. It should be interesting, engaging, aesthetically pleasant, and technically well-formed in terms of HTML structure, character set encoding, and other guidelines specific to emails (for instance, avoid CSS styles and use inline styles, avoid JavaScript code, etc.). Remember that your emails are perceived as extensions of your brand not only to your recipients but also to ISPs monitoring email deliverability.

Modern email marketing tools provide rich personalization and dynamic content functionality that enables you to reach each and every one of your recipients with fully personalized content. Combine this with a professional sending infrastructure as described earlier and you will be able to contact your recipients with precision and at scale, delivering the right message to the right subscriber at the right time seamlessly over millions of contacts.

When you create your content ensure that you don’t:

  • Render all your text as images. ISPs monitor the ratio of text vs. images in an email. Furthermore rendering text as images impacts the size of the plain text version, too.

  • Create links using IP addresses, like Rather, host your pages on a human readable domain to distinguish yourself from spammers.

  • Have invalid (broken) links. Broken links will result in higher spam complaints and damage your sending reputation.

Microsoft Dynamics Marketing – your one-stop solution to all your volume email needs

Microsoft Dynamics Marketing provides support for most of the issues and challenges involved with sending volume emails discussed here. Dynamics Marketing provides:

  • A world-class, secure server infrastructure for volume email sending, including:

    • Compliance with Microsoft Secure Development Lifecycle and other security standards

    • Email Authentication, “postmaster” and “abuse” mailboxes for all domains

    • Correct configuration of all sending domains

    • Feedback loops established with all major ISPs

    • Pools of IP addresses based on reputation and purpose (transactional or promotional). In the upcoming releases it will be possible to request private IP addresses (requiring approval from Microsoft)

    • Capability to send transactional emails with complete traceability

  • An integrated email marketing environment with:

    • Built-in validation of subscription center and sender address text mandatory in every promotional email

    • A rich set of personalization and dynamic content capabilities

    • Validation rules prior to email sending, including detection of blacklisted URLs in an email, plain text version, etc.

    • Automatic handling of hard bounces

  • A dedicated team focused on supporting deliverability issues for our customers with:

    • Constant monitoring of deliverability indicators

    • Proactively addressing and solving deliverability issues

More information: Get started with email marketing messages

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