Fastmail incident

Replies sent using masked email addresses are bouncing

Minor Resolved

Fastmail experienced a minor incident on September 23, 2026 affecting Mail delivery, lasting 11h 12m. The incident has been resolved; the full update timeline is below.

Started
Sep 23, 2026, 08:00 PM UTC
Resolved
Sep 24, 2026, 07:12 AM UTC
Duration
11h 12m
Detected by Pingoru
Sep 23, 2026, 08:00 PM UTC

Affected components

Mail delivery

Update timeline

  1. investigating Sep 23, 2026, 08:00 PM UTC

    We're currently experiencing an issue where replies sent from masked email addresses are bouncing with an error instead of being delivered. Our team is investigating the issue. As a workaround, please add the email address you're looking to send emails from under Settings → My email addresses. You'll then be able to send emails from that address.

  2. identified Sep 24, 2026, 06:48 AM UTC

    Our developers have identified the issue and are working towards a fix.

  3. resolved Sep 24, 2026, 07:12 AM UTC

    Our developers have resolved the issue. An update we made wasn't fully applied, causing messages sent from masked email addresses to bounce. If you were affected, you can resend any messages that bounced.