Email Deliverability Best Practices for SaaS Businesses

Email is a lifeline for SaaS businesses – it’s how you welcome new users, reset passwords, send notifications, and keep customers engaged through newsletters or updates. Ensuring these emails actually reach the inbox (and not the spam folder) is known as email deliverability. In this guide, we’ll explain what email deliverability means, why your domain reputation is crucial, and outline best practices for both transactional emails (e.g. signup confirmations, receipts) and marketing emails (e.g. newsletters, promotions).

What is email deliverability?

Email deliverability refers to where your email ends up once it’s accepted by the recipient’s mail server – ideally, the main inbox rather than spam or other tabs. It’s distinct from basic email delivery, which only means the email was received by the server (even if it landed in spam or a promotions folder). In short, deliverability measures your ability to get emails into the inbox, not just into the system.

For SaaS businesses, deliverability is incredibly important. Poor deliverability directly impacts user onboarding, activation, retention, and conversion.

Deliverability is influenced by several factors:

• Sender reputation (domain and IP)
• Authentication (SPF, DKIM, DMARC)
• Bounce and complaint rates
• Message content and structure
• Engagement metrics (opens, clicks, deletions, replies)

Domain reputation – Why it matters for email deliverability

One of the most important factors in deliverability is your sender reputation.

As detailed in Sidemail’s article on domain reputation, mailbox providers now evaluate sender identity primarily at the domain level. Domain reputation refers to how email providers like Gmail or Outlook view the sending domain (the part after the @ in your email). 

In the early days of email, reputation was tied mostly to the server IP address, but modern spam filters have shifted focus to the sender’s domain as a more stable and long-term identifier. Unlike IPs (which can be changed or shared easily), a domain sticks with you – if your domain builds a bad reputation, switching IPs won’t fully escape that history. Conversely, a good domain reputation can carry over even if you change email providers or IPs.

Major mailbox providers have their own algorithms, but all look at similar domain reputation signals: 

• user spam complaint rates, spam trap hits, bounce rates (sending to invalid addresses), 
• sending consistency – avoiding sudden large spikes in volume, 
• user engagement with emails  – opens, clicks vs. deletions,
• authentication – a domain must be authenticated (via SPF/DKIM) before it can accrue a reputation. 

Maintaining a strong domain reputation requires consistent, authenticated sending to opted-in recipients, monitoring of bounce and complaint rates, and avoiding blacklists.

Best practices to improve email deliverability

Improving and maintaining high email deliverability requires attention to both technical setup and sending behavior. The following best practices apply to both transactional emails (e.g. account confirmations, password resets, receipts) and marketing emails (newsletters, promotions) – with some special notes for each where relevant. By implementing these, tech teams can greatly increase the chances that their emails hit the inbox reliably.

1. Authenticate your emails (SPF, DKIM, DMARC)

Setting up email authentication is step one for deliverability. SPF and DKIM are DNS records that prove your server is allowed to send on behalf of your domain, and they attach a cryptographic signature to each message. ISPs check these; without them, your emails are far more likely to be flagged or rejected. Moreover, as noted above, inbox providers will only build a reputation profile for your domain if your emails are authenticated.

Implementing DMARC on top (with a policy to monitor or reject unauthorized mail) adds another layer of trust and helps prevent others from spoofing your domain. 

In short, authentication establishes your identity and is foundational for good deliverability.

2. Use a reliable email sending infrastructure

The platform and IP address you send from can influence deliverability. If you’re using an Email Service Provider (ESP) or SMTP service, choose one with a strong track record for inbox placement. Providers that specialize in transactional email or have quality IP pools can give you a head start on reputation.

If you send large volumes of email, consider using a dedicated IP address that isn’t shared with other senders – this way, your reputation won’t be affected by other senders. Just remember that a new dedicated IP needs warming up.

3. Warm up new domains and IPs gradually

If you have a brand new sending domain or IP, don’t send a massive blast on day one. Inbox providers notice big, sudden volumes from new senders and may throttle or filter you. 

Start by sending small amounts of email and slowly increase over days or weeks. This “warming up” period allows you to build a positive sending history. During warm-up, focus on sending to your most engaged and friendly recipients (e.g. recent sign-ups, customers likely to open), which maximizes positive engagement signals. 

Over time, as you prove to mailbox providers that your domain sends wanted emails, you can scale to your full volume.

4. Segment transactional and marketing emails

It’s a best practice to separate your transactional traffic from marketing or bulk emails.

Why? Transactional emails (like sign-up confirmations and receipts) are usually highly important, expected by the user, and have near 100% valid recipients. 

Marketing emails, on the other hand, go to broader audiences, may not be opened as frequently, and carry a higher risk of spam complaints or unsubscribes. Ideally, use a separate sending subdomain (or even a separate IP) for marketing campaigns so that your core product emails are isolated.

5. Keep your email list clean and opted-in

A healthy mailing list is essential for deliverability. Always use opt-in methods for sending marketing emails to ensure recipients actually want your emails – never buy lists or scrape emails, as those addresses will lead to high bounces and spam complaints. 

Over time, regularly clean your list by removing or segmenting unengaged subscribers. If someone hasn’t opened or clicked your emails in many months, continuing to send to them only risks them hitting spam or dragging down your engagement rates. Also, promptly remove addresses that hard-bounce (invalid emails) or consistently soft-bounce.

By emailing only people who expect (and interact with) your messages, you send a strong signal to inbox providers that your emails are wanted.

6. Send relevant content and encourage engagement 

Beyond the technical factors, the content you send and how users react to it plays a big role in deliverability. Make sure your email content is valuable and relevant to the recipient. 

For marketing emails, personalize where possible, segment your audience so they receive content that matches their interests, and avoid gimmicky or spammy tactics. High-quality content leads to higher open rates and clicks, which in turn boosts your sender reputation. 

Also, make emails readable on all devices and avoid elements that might trigger filters (very large images with little text, deceptive subject lines, etc.). 

Another tip: avoid no-reply sender addresses – using a real reply-to address (or even inviting replies) can improve engagement and signals that you’re open to communication.

Critically, you should make it easy for users to unsubscribe or manage their email preferences. It might feel counterintuitive to voluntarily offer an easy opt-out, but it’s far better than the alternative: if a user wants off your list and can’t do so easily, they will likely report your email as spam. Those spam reports directly damage your deliverability. By having a visible unsubscribe link and honoring removals immediately, you keep your list full of people who genuinely want your emails. This also indirectly boosts your open and click rates (since uninterested people are gone), which improves reputation. 

Remember, mailbox providers are watching how users interact – if they consistently ignore or delete your emails, or worse, flag them, that will hurt your deliverability. Engaged recipients (opening, clicking, replying) are the goal.

7. Monitor your sender reputation and performance 

Treat deliverability as an ongoing effort, not a one-time setup. Continuously monitor key metrics: your inbox placement rate (what percent of emails go to inbox vs. spam), open rates, click rates, bounce rates, and complaint rates. If you use services like Google Postmaster Tools, watch your domain reputation trend and any spike in spam reports

Many ESPs provide dashboards with metrics; drops in delivery or engagement can signal an issue to investigate. By catching problems early, you can adjust before they seriously damage your domain’s standing. In short, monitor what you send. As the saying goes, “you can’t improve what you don’t measure.” Stay vigilant and treat your sender reputation as a valuable asset.

What is a “good” email deliverability rate?

Email deliverability isn’t a simple yes/no metric, so what counts as a “good” rate? It can vary by industry and the type of email, but generally, you want the vast majority of your emails reaching inboxes. In practice, many email marketers consider an inbox placement rate above ~90% to be very good, and anything around 95% or higher as excellent.

Transactional emails, which are often sent to verified addresses (e.g. users who just signed up or are expecting the email), should ideally hit even closer to 100% deliverability – these are critical messages, and with proper practices, nearly all should go through.

In summary, “good” deliverability means the vast bulk of your emails reliably reach the inbox. Aim for as close to 100% as you can, but if you’re hitting ninety-something percent consistently, you’re on the right track. Always be cautious if that number starts slipping down.

Tools and platforms to help with deliverability

Achieving great deliverability is a combination of good sending practices (as discussed above) and using the right tools. Many SaaS teams rely on dedicated email delivery services or platforms (ESP – Email Service Providers) to handle the heavy lifting of sending emails at scale. These platforms not only provide email APIs and SMTP servers, but often they manage underlying things like IP reputation, feedback loops, and compliance, which can significantly affect your deliverability. Here’s a brief overview of a few popular email delivery tools and how they stack up:

• Sidemail.io: Tailored for startups and SaaS companies, Sidemail focuses on simplicity, deliverability, and ease of use. It specializes in transactional email – things like sign-up confirmations, password resets, and onboarding sequences – and helps ensure those critical messages are delivered fast and reliably. But also offers everything that startups need for sending marketing emails and setting up email automations. One standout advantage is that Sidemail handles infrastructure, IP reputation, and warm-up automatically, which is especially valuable for teams without dedicated email ops staff. It also provides great developer ergonomics with clean APIs and a streamlined UI. If you want a high-deliverability transactional email platform without deep configuration, Sidemail is an excellent choice. 
• Mailgun: Mailgun is a powerful, developer-centric email delivery service that combines robust API access with comprehensive tools for deliverability and analytics. It's designed for businesses that need granular control over email infrastructure, from SMTP to advanced routing and tracking. What makes Mailgun particularly valuable for SaaS is its real-time email validation, inbox placement testing, dedicated IP options, and predictive email analytics. Though it requires more technical overhead, Mailgun provides solid flexibility and insight.
• SendGrid: One of the largest email infrastructure providers, now part of Twilio. SendGrid is a popular all-in-one platform that offers both transactional and marketing emails through a scalable cloud infrastructure. It provides a lot of advanced features and analytics. It’s also known for its free tier.
• Amazon SES (Simple Email Service): Amazon SES is a powerful, low-cost email-sending platform from AWS, ideal for SaaS companies with technical teams that want full control over their email infrastructure. It supports both transactional and marketing emails at scale, offering high deliverability potential when properly configured. While it requires more technical effort than platforms like Sidemail, Mailgun or Sendgrid, SES offers unmatched flexibility and scalability for teams willing to handle its configuration overhead.

Regardless of which platform you choose, remember that the tool is just one part of the equation. A good ESP can give you a strong foundation, but your sending practices are still crucial. If you send spammy content or blast unengaged lists, even the best platform won’t save your emails from the spam folder. Conversely, with excellent practices, even a decent platform can yield great deliverability. Ideally, pick a platform that aligns with your needs and follow the best practices outlined earlier. 

Closing thoughts

Email deliverability is part art, part science. For SaaS founders and tech professionals, it pays to understand the fundamentals: build your domain’s reputation through responsible sending, set up the proper technical authentication, and always keep the recipient’s experience in mind (sending relevant, wanted emails). 

High deliverability means your users get the information they need – when they need it – fostering trust and engagement with your product.

In summary, email deliverability matters because your relationship with users depends on reliable communication. Treat your sending domain’s reputation as a valuable asset, stick to proven practices, and choose tools that support your goals. Do that, and you’ll greatly increase the odds that your next critical message lands right where it belongs – at the top of your user’s inbox, ready to be read.