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What is Fastmail Bot?

Direct Answer: Fastmail bot for image proxying and calendar fetching, operated by Fastmail.

Operator: Fastmail Type: Social Media Bot Purpose: Image proxying and calendar data fetching for user syncing

The Fastmail bot connects to external servers on behalf of users for image proxying and calendar fetching/syncing. It uses specific user agent strings to identify itself, enhancing user privacy by obscuring their user agent and IP address.

User-Agent Identification

The following user-agent strings identify Fastmail Bot in your live traffic data:

  • FastmailUA/1.0
  • Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.5993.117 Safari/537.36 FastmailUA/1.0

robots.txt Rules for Fastmail Bot

Respects robots.txt: No

This bot does not commit to following robots.txt

Fastmail Bot does not officially follow robots.txt directives. The only reliable way to control access is through server-side blocking (IP filtering, user-agent rules in your web server config) combined with log monitoring to verify effectiveness.

Need continuous verification across 500+ bots? Can AI See It automates this.

Crawl Behavior

Frequency:On-Demand

Request Pattern:Requests For Image Proxying And Calendar Data Fetching

Official Documentation Quotes

"We identify ourselves when we do so in the `User-Agent` header field sent with the HTTP request."

"To achieve maximum compatibility, the user agent for this bot appears (mostly) as a common browser user agent string, with “FastmailUA/1.0” appended."

Crawl Activity Index

Relative crawl activity for Fastmail Bot over the past 28 days. Higher values indicate increased crawling intensity compared to the period baseline.

View recent activity data (last 7 days)
Date Activity Index
Mar 26, 2026 88.0
Mar 27, 2026 82.7
Mar 28, 2026 83.1
Mar 29, 2026 81.8
Mar 30, 2026 87.3
Mar 31, 2026 90.2
Apr 1, 2026 88.9

Source: Cloudflare Radar

Why track Fastmail Bot traffic?

Ensure your link previews render correctly. Fastmail Bot fetches your pages to generate link preview cards on Fastmail. If it can't access your meta tags, your shared links display broken or generic previews.

Monitor social sharing activity. Fastmail Bot requests correlate with how often your URLs are being shared on Fastmail, even before engagement metrics are available.

Log Verification

To verify Fastmail Bot traffic in your live traffic data:

  1. Search access logs for the user-agent strings listed above
  2. Check if the IP addresses match documented ranges (if provided by Fastmail)
  3. Verify the crawl pattern matches documented behavior
  4. Use reverse DNS lookup for additional verification if available

Note: Observed behavior in production environments may differ from official documentation. Live traffic monitoring provides the only reliable verification of actual bot behavior.

Undocumented Information

The following information is not officially documented for Fastmail Bot:

  • crawl frequency details
  • IP verification method

Verify your link previews work — and track social bot access

  • Confirm Fastmail Bot can access your Open Graph meta tags
  • Track which URLs are being shared on Fastmail
  • Detect failed fetches causing broken preview cards
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Official Documentation

View Official Fastmail Bot Documentation →

Information sourced from official documentation. Content generated with AI assistance.