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Fastmail Bot

Fastmail fetch and image proxy bot.
FastmailFastmailUA
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What is Fastmail Bot?

FastmailUA covers two kinds of server-to-server traffic from Fastmail. When a Fastmail user opens a message containing an external image, Fastmail loads and proxies that image. Fastmail also uses the identity to fetch subscribed ICS feeds and synchronize remote CalDAV calendars.

The image proxy keeps the recipient's browser cookies out of the origin request and hides the recipient's IP address. It sends a browser-like user agent ending in FastmailUA/1.0. Calendar requests use the shorter FastmailUA/1.0 value and can recur as Fastmail keeps a subscription synchronized.

A FastmailUA hit does not mean the requester is crawling a page for search. It may record an email image being viewed or a calendar being refreshed. Neither workflow is documented as AI search, model training, or answer generation, so this traffic has no supported AI visibility claim.

Fastmail publishes FastmailUA as the substring common to its related user agents. Robots.txt support is not confirmed in the bot metadata, and Cloudflare says the identity does not follow robots.txt. The record offers no verified IP status or request signature.

Indirectly relevant

Is Fastmail Bot relevant for AI search?

Indirectly. Fastmail Bot has no AI product of its own, but its output can end up in the systems that AI answers draw on.

Fastmail Bot fetches pages to build link-preview cards. It does not feed an AI index, but it reads the same Open Graph and structured metadata that AI systems parse to understand your pages, so clean preview metadata doubles as AI-friendly metadata.

How to handle Fastmail Bot

Permit FastmailUA on public email images or calendar feeds that Fastmail users are meant to load. If a calendar is private, require the same authenticated CalDAV access that any other client needs. Do not open a protected feed solely because the header names Fastmail.

This robots.txt group states a preference for the stable token:

User-agent: FastmailUA
Disallow: /

The available records do not confirm that FastmailUA will honor it, and Cloudflare's bot directory marks compliance false. Use application, CDN, or firewall rules if requests must be rejected. Blocking the image proxy can leave external images unavailable to Fastmail readers, while blocking a feed can stop its synchronization.

Examples

  • A newsletter image server sees a browser-style request ending in `FastmailUA/1.0` when a recipient opens the message in Fastmail.
  • A public events calendar receives periodic `FastmailUA/1.0` requests after a user subscribes to its ICS feed.

Frequently asked questions about Fastmail Bot

Learn about AI visibility monitoring and how Promptwatch helps your brand succeed in AI search.

Fastmail loads external images through its servers so the origin does not receive the reader's IP address, browser user agent, or browser cookies.

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