Why are random characters added to URLs in email click tracking?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 May 2025
Updated 15 Aug 2025
6 min read
When you receive an email, you've likely noticed that the links sometimes look a bit different from the original URL. Instead of a straightforward website address, you see a jumble of seemingly random characters, often preceded by a different domain than the one you expected. It's a common sight, and it often leads to questions about what these characters mean and whether they pose a security risk.
These additional characters and domain changes are usually part of a sophisticated system designed to track how you interact with an email. While they might appear suspicious at first glance, they are typically a legitimate component of email marketing and analytics. However, understanding their purpose and how they work is crucial for both email senders and recipients, especially given the rising concerns about phishing and data privacy.
Understanding email click tracking
Email click tracking is a fundamental tool for understanding the effectiveness of email campaigns. Instead of directly linking to the destination, Email Service Providers (ESPs) or marketing platforms wrap each link in an email with their own tracking URL. When a recipient clicks on this modified link, the click is first registered by the ESP's server before the recipient is redirected to the intended destination.
This process allows senders to gather valuable data, such as how many people clicked a specific link, which links were most popular, and even the geographic location of the click. This data is vital for optimizing future campaigns, personalizing content, and understanding audience engagement. Without click tracking, marketers would largely be blind to the direct impact of their email efforts.
Many email providers, like Mailjet, transparently explain that links sent through their service are wrapped for tracking purposes. This functionality is generally standard practice across the industry. Email link tracking works by adding unique tags to each link in an email. When a recipient clicks the link, the tags route them to the original destination after recording the click, as outlined in a MailSuite article.
Decoding the tracking parameters
The "random" characters you see appended to URLs are far from random. They are carefully constructed, encoded strings of data. These strings typically contain a variety of information that allows the ESP to identify the specific email, recipient, campaign, and even the exact link that was clicked. This granular data is what powers the analytics dashboards marketers rely on.
Common data embedded in these tracking parameters includes a unique recipient ID, a campaign ID, a specific link identifier, and sometimes a timestamp or a security token. These parameters often use standard encoding methods like URL encoding or Base64 to ensure that the data can be transmitted reliably within a URL structure, even if it contains special characters.
For example, Google Analytics parameters are a well-known example of these strings that indicate cross-domain tracking. These parameters are crucial for linking a click back to the specific email and recipient, providing the sender with comprehensive analytics. The structure of these URLs can vary significantly between different ESPs, but their underlying purpose remains consistent: to track engagement efficiently and accurately.
Security and deliverability implications
While legitimate, these complex URLs can sometimes raise red flags, both for recipients and for automated email filters. Recipients might view unusual links with suspicion, especially if they are not familiar with email tracking practices. More critically, email filters and security systems closely examine URLs for any signs of malicious intent.
Spammers and phishers often exploit the complexity of URLs, using similar obfuscation techniques to hide malicious destinations. A phishing link can look very weird with many special characters to trick users. This can lead to legitimate tracking links being incorrectly flagged as suspicious by spam filters or even being added to blocklists (or blacklists). If your tracking domain (or even the IP address) ends up on a major blocklist, your emails could face significant deliverability issues, leading to messages landing in spam folders or being rejected outright. This highlights the importance of blocklist monitoring.
Broken links
One unexpected issue can arise if the tracking URL itself becomes malformed or is incorrectly parsed by certain email clients or systems. This can happen if the email template's plain text version misinterprets the HTML link, leading to extra characters being appended or truncated. For example, some systems might mistakenly include closing brackets or adjacent text from the email content, rendering the link unusable or redirecting to an incorrect page.
Such issues are not consistent and can appear randomly across different ISPs, users, or links, making them challenging to diagnose. This can negatively impact your click-through rates and overall campaign performance. It's a key reason why testing your emails across various environments, especially plain text rendering, is essential.
To ensure your email campaigns perform optimally and avoid deliverability pitfalls, adhering to best practices for managing tracking URLs is essential. This includes technical configurations and careful testing of your email content.
Email configuration best practices
Use Custom Tracking Domains: Configure a custom tracking domain that aligns with your sending domain to improve trust and deliverability. This helps avoid issues where your tracking links might be blocklisted if they share a generic ESP domain.
Ensure Proper URL Encoding: Ensure your ESP properly encodes all URL parameters. Malformed or unencoded URLs can cause deliverability issues and break links.
Monitor Tracking Domain Reputation: Regularly check the reputation of your tracking domains. If they appear on email blacklists (or blocklists), address the issues immediately.
Diligent testing is a cornerstone of good email practice. Before sending your campaigns, it's advisable to perform comprehensive email deliverability tests. This includes checking how your links render in both HTML and plain text versions across various email clients (such as Outlook, Gmail, and Apple Mail). This proactive approach helps identify and rectify any unexpected character additions or link breakage before your campaign reaches your subscribers.
Navigating the complexities of email links
The seemingly random characters in email URLs are a sophisticated mechanism for click tracking, providing crucial insights for email marketers. While they are a standard practice, their presence can sometimes lead to deliverability challenges, including misidentification by spam filters or unexpected link breakage in certain email clients. By understanding their purpose and implementing best practices like using custom tracking domains and thorough testing, senders can ensure their emails reach the inbox and their campaigns remain effective.
Views from the trenches
Best practices
Always use a custom tracking domain that aligns with your sending domain to build a strong reputation and avoid generic blocklists.
Regularly test your email links across various email clients and devices, paying close attention to both HTML and plain text rendering.
Ensure your email service provider correctly encodes URLs, preventing issues like extraneous characters or broken links.
Segment your audience and personalize content to reduce the likelihood of emails being marked as spam, which can impact link reputation.
Common pitfalls
Ignoring the plain text version of your emails, which can lead to malformed URLs and unexpected character additions in some email clients.
Not monitoring your tracking domain's reputation, leaving you unaware if it's been added to a blocklist, causing deliverability issues.
Using generic tracking domains that are shared by many senders, increasing the risk of being affected by others' poor sending practices.
Failing to conduct comprehensive pre-send tests, missing critical errors in URL construction or redirection that impact user experience.
Expert tips
Implement consistent URL structures across all campaigns to help recipients recognize legitimate tracking links and build trust.
Educate your team on how email tracking works, reducing internal confusion and improving troubleshooting efficiency.
Leverage DMARC reporting to gain deeper insights into how email providers handle your tracked links and identify potential issues.
Consider link cloaking for sensitive campaigns to enhance security and prevent direct exposure of tracking URLs.
Marketer view
Marketer from Email Geeks says they found the issue was happening only to users who opened the email as plain text. The template editor generated plain text versions where each URL was wrapped by curved brackets with no space afterwards, sometimes capturing the next word.
2020-11-04 - Email Geeks
Expert view
Expert from Email Geeks says that this behavior strongly suggests a code issue, either within the email itself, the Email Service Provider's side (like SendGrid), or the tool used to view the click tracking data.
Outlook, 
Gmail, and 
Apple Mail). This proactive approach helps identify and rectify any unexpected character additions or link breakage before your campaign reaches your subscribers.
