What is FastmailUA?
FastmailUA is Fastmail's content fetcher and image proxy service that retrieves external images and content for email security. It protects users from tracking pixels and malicious content by proxying external resources through Fastmail's secure servers. You can set up Agent Analytics to see when FastmailUA visits your website.
Overview
| Operated By | Fastmail |
| Source | Official Website |
| Expected To Follow Robots.txt | No |
| Insights Last Updated | September 15, 2026 |
Do you operate this agent? Contact us to suggest an update.
Category
Expected Behavior
FastmailUA usually makes a single request within seconds of a URL being shared, without crawling further. Traffic rises and falls with sharing activity, so a widely circulated link can produce a sharp burst of fetches.
FastmailUA's User Agent
| User Agent | Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.5993.117 Safari/537.36 FastmailUA/1.0 |
How To Block FastmailUA With Robots.txt
Add this rule to your robots.txt file to request that FastmailUA not access your website, or use Automatic Robots.txt to request the same of all fetchers at once. You can customize which pages are blocked by swapping out / for a different path.
User-agent: FastmailUA # https://knownagents.com/agents/fastmailua
Disallow: /Insights for FastmailUA
As of September 15, 2026, this data reflects agent visits measured across thousands of websites using Agent Analytics, combined with daily scans of the top 1000 websites and their robots.txt files.
Robots.txt Blocked Percentage
Country of Origin
Robots.txt Blocking Trend
7% of top websites block FastmailUA in their robots.txts.
Overall Fetcher Traffic
1.8% of all web traffic came from fetchers.
Top Visited Website Categories
The types of websites most frequently visited by FastmailUA.
Frequently Asked Questions
Should I Block FastmailUA?
Usually not. Blocking FastmailUA may leave shared links without a title or image, making them less inviting to click. If it begins fetching at unexpected volume, try rate limiting before blocking it outright. For context, 7% of the top websites we track currently have robots.txt rules for FastmailUA.
Does FastmailUA Follow Robots.txt Rules?
No. FastmailUA is not expected to follow robots.txt rules, so a disallow rule only communicates your preference. Enforce the block with firewall or server rules, then use Agent Analytics to verify that its requests stop.
Does FastmailUA Access Private Content?
No. FastmailUA has no credentials and should access only the public URL and assets needed for a preview. It does not continue through the rest of your site.
How Can I Tell if FastmailUA Is Visiting My Website?
Agent Analytics tracks FastmailUA visits in real time. You can also check your server logs for requests whose user-agent string contains "FastmailUA". Look for a page and its preview assets being requested without follow-up navigation. Because FastmailUA does not publish a verification method, any client can claim its identity and a log match is only a clue.
Why Is FastmailUA Visiting My Website?
Someone shared a link to your page. FastmailUA fetched it to build a preview card, and each new share may trigger another request. A spike often means your content is circulating more widely.