Getting started with email deliverability
In short: email deliverability is the ability to land your campaigns in your contacts’ inboxes rather than the spam folder, and it accounts for about half of a campaign’s success. Getting it right means pairing a well-crafted campaign with a healthy sender reputation, authenticated sending (SPF, DKIM, and DMARC), clean mailing lists, and an easy one-click unsubscribe.
Identifying the needs and interests of contacts and conceptualizing email campaigns around those are part and parcel of a marketer’s daily routine. Sometimes marketers may assume that crafting a compelling campaign alone will help them hit their conversion goals. This assumption is partially correct. However, marketers will have to do a lot more than just crafting a nice campaign — they will also have to work to land it in the inbox. Once a campaign is successfully delivered, the campaign’s content takes over and helps you meet your conversion goals. So achieving these is a two-step process: you first work to create a compelling campaign, then work even harder to land it in your recipient’s inbox.
The ability to land your campaigns in your contact’s inbox is called email deliverability. This is a crucial factor that accounts for half of your campaign’s success. To understand it, we’ll look at how Zoho Campaigns’ email infrastructure works, how mailbox providers make inbox decisions, and the efforts anti-spam services and mailbox providers take to curtail spam.
Email infrastructure
At Zoho Campaigns, we’ve built a super-efficient email infrastructure that helps us offer seamless delivery of marketing emails. The core of our email infrastructure comprises the sender domain, IP address, and the anti-spam engine.
Sender domain
Your sender domain’s reputation plays a major role in achieving inbox placement. When mailbox providers receive emails, they assess the sender domain’s reputation to make inbox decisions. If the sender domain has a positive reputation, the chances of achieving inbox placement are high; if it has a negative reputation, the emails may land in the spam folder.
At Zoho Campaigns, we urge our users to ensure their sender domain always earns a positive reputation from mailbox providers and anti-spam services. The best way to start is by authenticating the sender domain.
Domain authentication
Authenticating your sender domain with SPF, DKIM, and DMARC is no longer just a best practice — since February 2024 it is required for anyone sending in bulk, and it is the foundation of a positive sender reputation.
One of the major challenges in the email marketing industry is spam. To counter it, businesses adopt several security mechanisms. One such technique is domain authentication — the process of authenticating the sender domain by implementing a set of validation mechanisms. SPF, DKIM, and DMARC are the most commonly implemented ones, and they are now effectively mandatory: under Google and Yahoo’s bulk sender requirements for senders of 5,000+ messages a day, you must authenticate with SPF and DKIM and publish a DMARC policy of at least p=none, with the From domain aligned. Microsoft applies the same expectations to Outlook.com senders. A stronger DMARC policy (p=quarantine or p=reject) is the recommended target once your reports look clean.
Spammers often purchase a domain and start blasting email without authenticating it, so unauthenticated mail resembles spam to mailbox providers. Authenticating your sender domain ensures the emails you send aren’t tampered with in transit, earns a positive reputation from mailbox providers and anti-spam services, and improves your chances of inbox placement.
Using a new sender domain
At Zoho Campaigns, we recommend you don’t send a huge volume of email from a new sender domain, because a new domain has no reputation with mailbox providers — and providers treat mail from an unknown domain as suspicious. When you decide to use a new sender domain, warm up the sender domain first: send a few emails to start and slowly increase the volume based on how recipients respond.
IP address
At Zoho Campaigns, you can choose between a shared IP address and a dedicated IP address based on your business requirements. The reputation of an IP address is a crucial factor mailbox providers assess before making inbox decisions, so we recommend you ensure your IP address always earns a positive reputation from mailbox providers and anti-spam services.
Using a dedicated IP address
When businesses migrate from a different email marketing service to Zoho Campaigns and opt for a dedicated IP address, we always urge them to warm it up first, because a fresh dedicated IP has no reputation with mailbox providers and anti-spam services. Send a few emails first and slowly increase the volume based on the response.
Anti-spam engine
At Zoho Campaigns, we have a powerful anti-spam engine that helps us identify and neutralize spam. Every campaign our users create is subjected to a stringent review before we approve it. Powered by state-of-the-art spam filters and algorithms, the engine scans the sender domain, email content, and the URLs used in a campaign to identify patterns that point to spam. When it identifies spam, it won’t approve the campaign and will block the user’s account.
Contact management
Mailing-list quality drives deliverability. Grow lists organically with double opt-in, segment them, and keep them clean so bounces, spam markings, and complaints stay low.
Mailing lists are the fundamental blocks on which email marketing is built, so we always recommend you grow them organically and maintain quality. The success of a campaign depends on the quality of the mailing list: if the quality is poor, your emails may bounce, receive spam markings, unsubscribes, or even complaints. To grow a healthy list, use the double opt-in technique — it eliminates the possibility of invalid email addresses and spam traps entering the list.
Once a contact enters the mailing list, segment the list and group contacts based on their needs, interests, and demographic factors like age and gender. After segmenting, use a target marketing strategy to offer content relevant to each contact’s needs and interests. As your lists grow, identify inactive contacts and win them back with re-engagement campaigns. The best way to keep a mailing list active is to keep contacts engaged and to clean your mailing list regularly — at least every six months — to remove dormant contacts.
Factors that affect deliverability
Now that we’ve covered the major components of email infrastructure, let’s focus on the factors that affect email deliverability.
Email bounce
When a sent email can’t be delivered, it’s an email bounce — an issue marketers face frequently. Though it sounds simple, a bounce seriously affects deliverability. There are two types of email bounce.
Soft bounce
A soft bounce is a temporary delivery failure that occurs when the recipient’s mailbox is full, the receiving server is down, and so on. When an email soft bounces, Zoho Campaigns retries delivery: if a soft bounce occurs, we attempt to resend the campaign seven more times; if it keeps failing, it is eventually reclassified as a hard bounce.
Hard bounce
A hard bounce is a permanent delivery failure. Common reasons are an invalid recipient address or an invalid domain. Hard bounces seriously damage the reputation of your sender domain and IP address, and a rising hard-bounce rate can get them blacklisted, so hard-bounced addresses should be suppressed immediately and never re-mailed. The underlying cause of most bounces is poor list management, so grow your list organically and prune it every six months.
Spam markings
Your contacts mark your emails as spam when they feel the content is irrelevant to their needs and interests. Spam markings are negative signals mailbox providers and anti-spam services watch for; each one incurs a negative reputation for your sender domain and IP address, and providers may then deny inbox placement for future emails. This metric now has a hard line attached to it: under the 2024 Google and Yahoo sender requirements, keep the spam-complaint rate reported in Google Postmaster Tools below 0.10% and never let it reach 0.30%, or your mail can be throttled or rejected.
Unsubscribes
Contacts hit unsubscribe when they feel they’re not getting the content they signed up for. Unsubscribes are negative signals about your content or sending practices, and mailbox providers weigh engagement when making inbox decisions — so a spike in unsubscribes can cost you inbox placement for future campaigns. Counterintuitively, making unsubscribing easy protects you: bulk senders are now required to include a one-click unsubscribe (the List-Unsubscribe header defined in RFC 8058) and to process those requests within two days. A visible one-click option keeps unhappy recipients from reaching for the spam button instead.
Complaints
An email campaign can receive complaints either directly or through a feedback loop.
Direct complaint
When email recipients contact us directly and submit a complaint, it’s a direct complaint. Whenever we receive one, we perform a grassroots-level analysis to understand what went wrong. If the complaint is valid, we’ll block the user’s account and ask them for a detailed explanation.
Feedback loop
When a recipient marks your email as spam, the mailbox provider informs the business if it has subscribed to the provider’s feedback loop service. When a business receives such a notification, we offer best practices and suggest they follow them. If the next campaign also receives spam markings, we’ll block the account and ask for a detailed explanation, reinstating it only if the explanation is valid.
Best practices to maximize deliverability
Apart from your sender domain, IP address, and mailing lists, your sending practices hugely impact your campaign’s performance. The best way to hit your conversion goals is to adopt these hygienic practices:
• Authenticate your sender domain with SPF, DKIM, and DMARC before you send — this is now required for bulk senders
• Include a clear one-click unsubscribe link, and honor unsubscribe requests within two days
• Keep your spam-complaint rate below 0.10% and never let it reach 0.30%
• Craft a campaign with a compelling subject line and a pre-header
• Offer content relevant to your contact’s needs and interests
• Don’t use spam phrases in the email content
• Aim for a balanced layout — roughly 60% text and 40% images — add descriptive alt text to every image, and avoid image-only emails
• Have an email footer
• A/B test your campaigns
• Analyze the recipient’s time zone before sending your campaign
• Don’t send a huge volume of emails without warming up the sender domain and IP address
• After sending, monitor the open rate, click rate, bounce rate, and conversions
• Reward your active contacts with discounts on their next purchase
• Win back inactive contacts by sending re-engagement emails
• Clean your mailing lists at least every six month
• Clean your mailing lists at least every six month