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. Agent Analytics can track when it visits your website.
Category
Expected Behavior
FastmailUA shows up within seconds of someone sharing one of your URLs, grabs the title, description, and preview image, and leaves. Expect one hit per share, no link following, and volume that tracks how much your content circulates. A widely shared link can mean thousands of fetches in an hour.
Overview
| Operated By | Fastmail |
| Expected To Follow Robots.txt | No |
| Insights Last Updated | July 6, 2026 |
Robots.txt Blocked Percentage
Country of Origin
Robots.txt Blocking Trend
As of July 6, 2026, 0% of top websites block FastmailUA in their robots.txt files.
Overall Fetcher Traffic
As of July 6, 2026, 3.8% of all web traffic came from fetchers.
Top Visited Website Categories
This data reflects agent visits measured across thousands of websites using Agent Analytics, combined with daily scans of the world's top 1000 websites and their robots.txt files.
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 |
Access other known user agents and IP addresses using the Enterprise API.
How To Block FastmailUA
Add this rule to your robots.txt file to request that FastmailUA not access your website. You can customize which pages are blocked by swapping out / for a different path.
User-agent: FastmailUA # https://knownagents.com/agents/fastmailua
Disallow: /Frequently Asked Questions
Should I Block FastmailUA?
No. FastmailUA builds the link preview that appears when someone shares your page in a chat or social feed. Blocking it turns those shares into bare links with no title or image, which fewer people click. Its traffic normally follows sharing activity rather than a crawl schedule, so if it ever starts crawling at volume, rate limit it instead of blocking it. Almost none of the top websites we track have robots.txt rules for FastmailUA right now.
Does FastmailUA Respect Robots.txt?
No. FastmailUA is not expected to honor robots.txt, so a disallow rule only states your preference. Enforce the block with firewall or server rules, then confirm in Agent Analytics that its requests actually stop.
Does FastmailUA Access Private Content?
It cannot. FastmailUA loads only the exact URL someone shared, reads the title, description, and preview image, and leaves. It has no credentials and does not follow links to other pages.
Why Is FastmailUA Visiting My Website?
Someone shared a link to your page. FastmailUA fetched it once to build the preview card, and every new share can trigger another fetch, so spikes mean your content is spreading.
How Can I Tell if FastmailUA Is Visiting My Website?
Agent Analytics tracks FastmailUA visits in real time alongside every other known AI agent, crawler, and scraper. You can also check your server logs for requests whose user agent string contains "FastmailUA". Look for hits on single pages moments after someone shares a link, with no crawling afterward. Keep in mind that FastmailUA doesn't publish a verification method, so any client can claim its user agent string and a log match is a hint rather than proof.