FastmailBot is a bot in the link preview bots category, operated by Fastmail.
Fastmail fetch and image proxy bot
Link preview bots fetch a page when someone shares its URL in a chat app or social network, to build the preview card. Blocking them breaks your link previews, so keep them allowed but leave them out of analytics and ad requests.
Sample user agent strings sent by FastmailBot:
FastmailUA/1.0Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.5993.117 Safari/537.36 FastmailUA/1.0Anyone can copy a user agent string. Transfon Security also checks where each request comes from, so a request that claims to be a known crawler but comes from the wrong network is treated as a fake, not as the real crawler.
We have not confirmed whether FastmailBot follows robots.txt. Add a rule, then check your logs to see that it stopped. robots.txt is a plain text file at the root of your domain, such as https://example.com/robots.txt.
User-agent: FastmailUA Disallow: /
User-agent: FastmailUA Disallow: /private/ Disallow: /search
User-agent: FastmailUA Allow: /blog/ Disallow: /
User-agent: FastmailUA Allow: / User-agent: * Disallow: /
User-agent: FastmailUA group, FastmailBot ignores your User-agent: * rules, so repeat any that should still apply.FastmailUA from FastmailBot's user agent; check Fastmail's own documentation if it publishes a different robots.txt name.Treat robots.txt as a statement of your policy, and enforce it where requests arrive.
FastmailBot fetches pages when your links are shared or syndicated. Keep it allowed so previews and feeds work, but leave it out of page views and ad requests.
Transfon Security for publishersWhen ads or posts are shared, FastmailBot fetches the landing page. Those hits are not clicks, so keep them out of campaign reports.
Transfon Security for advertisersProduct links shared in chats and feeds are fetched by FastmailBot. Keep it allowed so previews show the right image and price.
Transfon Security for e-commerceAllow FastmailBot on public pages so shared links preview well, and keep it off the app.
Transfon Security for SaaS and APIsrobots.txt is a request, not an enforcement. Transfon Security shows FastmailBot by name in the Top Bots report, so you can see how often it visits and which pages it reads. Block or allow it with a User Agent rule, or slow it down with a rate limit decision rule.
Transfon Security
FastmailBot is a bot in the link preview bots category, operated by Fastmail. Fastmail fetch and image proxy bot
We have not confirmed whether FastmailBot follows robots.txt. Add a robots.txt rule, then check your logs to see that it stopped, and block it by user agent if it did not.
Add "User-agent: FastmailUA" followed by "Disallow: /" to the robots.txt file at the root of your site. To enforce it, block requests whose user agent contains "FastmailUA" at your WAF. In Transfon Security that is one User Agent block rule.
No. robots.txt is voluntary, so FastmailBot may not follow it, and anyone can send FastmailBot's user agent, so a fake FastmailBot ignores your rule. Enforce the rule where requests arrive, at your WAF, and check the source network.
Link preview bots fetch a page when someone shares its URL in a chat app or social network, to build the preview card. Blocking them breaks your link previews, so keep them allowed but leave them out of analytics and ad requests.
Transfon Security identifies every bot in this directory in your traffic reports, flags fake search crawlers, and lets you allow, block or rate limit each bot.
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