Deliverability best practices - how to keep my email from going to the SPAM folder

Managing your contacts can be a daunting task, but there are some best practices and resources that can help. rezora has great tools for identifying active and inactive contacts, and with a few changes, you can see higher open rates and more of your emails landing in the inbox.

What Can Cause an Email to Go to Spam

Deliverability means taking steps to help your email reach the recipient's inbox. When you send an email, the receiving server runs a series of checks and decides how to handle it. It's not always a simple pass or fail: an email might land in the inbox with images blocked, get diverted to spam, or bounce entirely.

Since every email server uses its own criteria, it's not always possible to pinpoint exactly why an email was flagged. Still, there's a clear set of practices that make the biggest difference.

Authentication

Authentication is the single most important deliverability factor today, and the requirements have gotten stricter. Since February 2024, Google and Yahoo require anyone sending 5,000 or more emails a day to personal accounts to properly authenticate their mail with SPF, DKIM, and DMARC. As of late 2025, Google has moved from delaying non-compliant emails to rejecting them outright, and once a domain is classified as a bulk sender, that classification doesn't go away even if volume later drops. Microsoft has rolled out similar expectations for Outlook, Hotmail, and Live.com addresses.

What this means in practice:

• Use your company-provided email address to send, since it's tied to a domain with proper authentication settings.

• Confirm SPF and DKIM are configured for your sending domain. These prove that the server sending your email and the message itself are legitimate.

• Confirm a DMARC record exists for your domain, with at minimum a policy of p=none. This ties SPF and DKIM together and tells receiving servers what to do if a message fails authentication checks.

• Keep your spam complaint rate low, ideally well under 0.3%. If contacts are marking your mail as spam instead of unsubscribing, that has a direct and lasting effect on deliverability.

If you're not sure whether your domain meets these requirements, it's worth checking with whoever manages your company's DNS records, since this now determines whether your email arrives at all rather than just how it's ranked.

Safelisting rezora's sending servers

If your company, or one of your clients, has an IT department managing email through a platform like Microsoft 365 or Google Workspace, it can be worth having them safelist rezora's sending servers or IP addresses. This adds an extra layer of trust at the organization level, on top of individual recipients marking your mail as safe.

Safelisting helps, but it isn't a substitute for proper authentication. If your domain's SPF, DKIM, and DMARC aren't set up correctly, safelisting an IP address may not reliably improve delivery on its own, and some IT teams will want to confirm authentication is in place before agreeing to safelist a vendor at all. Think of it as one more layer on top of authentication, not a replacement for it.

If you'd like help getting your company's or a client's IT team set up with the information they need, reach out to support@rezora.com and the team can follow up with what's needed.

Content

Good content design matters for readability, but also for deliverability.

Images: Email servers can't scan image content well, only where it's located. An email that's mostly image, or one big image, reads as unscannable and is more likely to get blocked or sent to spam. Keep each image under 1 MB, scale images to roughly 600-800 px wide, and include a solid mix of real text alongside your images.

Subject lines and body text: Use normal sentence case, avoid special characters, and steer clear of obviously pushy phrases like "Click here now" or "Act now." That said, this matters less than it used to. Modern spam filters weigh engagement history and sender reputation far more heavily than specific keywords, so this is a small piece of the picture rather than the main one.

Links: Make sure every link is legitimate and working. Test each one before sending.

Video: Most email clients still don't support embedded video playback. Use an image linked to the video's hosting page instead.

Copy and paste: Pasting content directly from another source often brings along hidden formatting and code, not just the visible text. This can cause layout issues and raise red flags with spam filters. Paste as plain text and reformat instead.

Contacts

Your contact list itself plays a major role in your sending reputation.

• Confirm consent. Make sure each contact opted in and that you have a record of when. Encouraging new contacts to add your address to their contacts list also signals to their email provider that your mail is expected.

• Send a welcome email to new contacts as soon as they sign up.

• Never use purchased lists. They're full of stale or fake addresses and spam traps; they're not permitted in rezora, and they will damage your reputation quickly.

• Remove stale contacts. If someone hasn't engaged with your emails in the last six months, take them off your sending list. This protects your reputation with mailbox providers and improves your metrics for everyone else.

Reputation

Receiving servers evaluate three things every time you send: the reputation of your "from" address, your sending domain, and rezora's sending IP addresses.

Fewer bounces and spam complaints build a good reputation over time. More of either can quickly hurt it. rezora actively monitors and protects the reputation of its sending IPs, maintains a bounce list, and supports users in improving their own deliverability. But your own sending habits, list hygiene, and authentication setup are what the internet remembers about you specifically.

Happy sending!