Email Deliverability & Links

The links in an email carry domain reputation signals that spam filters evaluate. The wrong domain in a link can move a legitimate email from inbox to spam — regardless of the content quality.

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How Links Affect Email Deliverability

Email spam filters evaluate multiple signals to determine whether an incoming email belongs in the inbox or in spam. Among these signals, the domains used in links within the email body carry significant weight — because the majority of spam and phishing emails contain links, and the domains those links use have often been seen in previous spam.

Spam filter link evaluation works at several levels:

• Domain reputation. The link's domain is checked against spam and phishing reputation databases. A domain with a history of spam, phishing or malware distribution scores negatively. A domain with a clean history and established sending behaviour scores positively.
• Domain age. Newly registered domains with no reputation history are treated with suspicion — spam campaigns frequently use freshly registered domains.
• Domain consistency. Links whose domain does not match the email's sender domain or the brand identity in the email body create a mismatch signal. An email claiming to be from YourBrand with links to a generic shortener domain is suspicious.
• Link count and ratio. Emails with very high link-to-text ratios, or many links to the same destination, can trigger spam scoring independent of the link domains.

Shared Domains vs Branded Domains

The most practically important distinction for email deliverability:

A branded custom domain is the definitive mitigation for shared domain deliverability risk. When every link in your emails uses your own domain, your deliverability performance depends entirely on your own sending behaviour — not on the behaviour of other users of a shared domain.

ESP Tracking Domains and Independent Link Analytics

Most email service providers (ESPs) replace links in sent emails with tracking redirects on their own tracking domain — click.sendgrid.net, trk.mailchimp.com, links.em.yourmarketing.com. This enables the ESP to track link clicks within their own analytics.

The deliverability concern: these shared tracking domains are used by all customers of that ESP. A tracking domain that has been used in spam by other ESP customers may carry negative reputation.

Mitigations:

• Custom tracking domain in the ESP. Most ESPs allow customers to configure their own domain for the tracking redirect — replacing the ESP's shared tracking domain with the customer's own domain. This removes the shared reputation risk for the ESP tracking layer.
• Branded short links via Cuttly. Using Cuttly short links on a custom branded domain as the links in the email, with the ESP's link tracking disabled or supplemented. The link tracking happens at the Cuttly level on the branded domain — the ESP's tracking domain is not involved.

DMARC, DKIM, SPF and Link Deliverability

Email authentication protocols — DMARC, DKIM and SPF — authenticate the sending domain of an email. They operate at the email header level and are independent of link domains within the email body. However, email authentication and link domain hygiene are complementary deliverability investments: authentication proves the email came from the claimed sender; branded link domains reinforce that the links within the email also represent the sender's identity.

Hover Preview Trust

Beyond spam filter scoring, links in email affect recipient-level trust. Email clients display the destination URL of a hyperlink in the status bar or tooltip when the recipient hovers over it. A branded short link on the sender's own domain in this hover preview is consistent with the sender identity — reinforcing trust. A generic shortener domain or an ESP tracking domain in the hover preview is inconsistent and can reduce engagement rates.

Related Terms

• DMARC / DKIM / SPF
• Branded Links
• Spam Protection
• HTTPS & SSL
• Click Tracking