Many marketers track delivery rate, which only confirms a mail server accepted the email. True success lies in deliverability—the art and science of landing in the primary inbox, not the spam folder. This is an untrackable metric that you can only influence.
Moving to a new domain provider or having a tech person make unvetted changes can accidentally break CNAME records. This causes authentication (SPF, DKIM, DMARC) to fail, immediately sending your emails to spam, even if your reputation was previously perfect.
Switching to a new custom sending domain resets your sender reputation to zero, like a new credit score. You must gradually ramp up sending volume, starting with your most engaged subscribers first, to build a positive history with mailbox providers.
Mailbox providers value replies above all other engagement metrics. A reply signals a personal, two-way conversation, which is a powerful indicator that the recipient wants the email. This helps emails land in the primary inbox, not just avoid spam.
Email sender reputation is not permanent. If you stop sending to your list for approximately six months (180 days), mailbox providers will treat your domain as if it's brand new. You will need to warm up your sending domain again to avoid deliverability issues.
Historically, an ESP's reputation heavily influenced deliverability. Now, with sender authentication requirements from Gmail and Yahoo, reputation is tied directly to your sending domain. This means your reputation follows you between ESPs, and you are solely responsible for managing it.
Smaller senders (<5,000 subscribers) struggle to build a stable domain reputation due to low volume where a few spam complaints have an outsized impact. It's often better to leverage the established reputation of your ESP's domain until you have enough volume to manage your own.
Subscribers from networks have low intent and often don't remember signing up. Send a dedicated welcome email that shows exactly where the recommendation came from (e.g., with a screenshot) and provides a prominent unsubscribe link to prevent spam complaints.
When an email's file size exceeds 102KB, Gmail "clips" it, hiding the full message behind a link. Because the open-tracking pixel is typically in the email's footer, it doesn't load when a clipped message is opened, leading to severe under-reporting of your actual open rates.
Due to Apple's Mail Privacy Protection automatically loading tracking pixels, open rates are inflated and no longer accurately reflect individual actions. However, these auto-opens don't fire if an email lands in spam. Therefore, use open rates to monitor trends and detect deliverability problems.
AI tools increasingly summarize emails directly in the inbox, heavily influencing the decision to open. To ensure the summary is compelling, place the key takeaway, offer, or value proposition at the beginning of your email, rather than burying it after a long introduction.
Sending more often (e.g., from weekly to daily) amplifies engagement signals for mailbox providers. If a segment of your list is unengaged, you are now sending more frequent negative signals. To counteract this, you must tighten your list hygiene rules.