Letterhead Incident History

1. resolvedOct 22 · 22:19 UTC

   This incident has been resolved.

Reported by Letterhead on their status page.

1. resolvedOct 9 · 16:34 UTC

   We are ready to put this one to bed. Thank you for your patience, and apologies for the hassle.

Reported by Letterhead on their status page.

1. resolvedOct 6 · 00:09 UTC

   This incident has been resolved.

Reported by Letterhead on their status page.

1. ResolvedOct 6 · 00:09 UTC

   This incident has been resolved.

Reported by Letterhead on their status page.

1. postmortemSep 24 · 17:23 UTC

   Email delivery interruption, September 21, 2026

   Summary

   ‌On September 21, 2026, an automated delivery restriction by one of our upstream email partners temporarily interrupted newsletter sending. The interruption was administrative in origin not an infrastructure failure of Letterhead.

   ‌Approximately 700,000 emails were delayed. Sending access was restored at 1:35 p.m. Eastern, and all affected emails had been sent by 2:38 p.m., when we marked the incident resolved.

   ‌We are responsible for maintaining the provider arrangements on which our delivery depends. Although the interruption was administrative in origin, it affected the reliability of Letterhead's service. We apologize for the disruption and recognize that eventual sending does not undo the impact of delays to time-sensitive newsletters.

   ‌Customer impact

   ‌Affected customer newsletters experienced delayed sending while the restriction was active and during subsequent recovery. Approximately 700,000 emails were affected, and all were subsequently sent.

   ‌We recognize that delayed delivery can reduce the value of time-sensitive newsletters, even when all messages eventually go out.

   ‌During the incident, we advised customers that they did not need to manually resend affected newsletters.

   ‌Cause and contributing factors

   ‌The immediate cause of the interruption was an erroneous, automated  compliance restriction on delivery in the U.S. through the provider, which created the appearance of delays and outage with sending. Despite normal, ongoing communication between our team and the provider’s, an automated block was incorrectly applied.

   Emails injected by our system were preserved and stored in a queue until the issue was resolved.

   ‌Restoration required a separate account authorization process. Letterhead’s technical account contact could identify and escalate the restriction but could not independently close the issue, which relied on a European-based team with different working hours.‌

   The affected sends depended on the existing provider account. Letterhead supports multiple email providers, but that capability did not provide a fallback for these sends. Recovery depended on restoring sending access through the affected provider.

   Detection and response

   ‌Letterhead maintains operational alerting, paging, and around-the-clock on-call coverage. We identified the sending interruption before receiving the provider's automated notification and contacted the provider’s team at 8:28 a.m. Eastern.

   ‌The restriction remained active during this coordination despite assurance of immediate restoration. Reactivation was confirmed at 1:35 p.m., five hours and seven minutes after Letterhead’s initial escalation.

   ‌We reported recovery underway at 1:41 p.m. and continued monitoring while delayed sends completed. All affected emails had been sent by the public resolution at 2:38 p.m.

   Timeline

   ‌The initial escalation time does not establish the exact start of customer impact. The public resolution time confirms that all affected emails had been sent by then, rather than identifying the precise moment the last delayed email was sent.

   Original public incident updates

   What worked and what fell short

   • Letterhead detected the interruption before the provider's  automated notification or any customer send failures, and promptly engaged the technical account contact. The affected sends subsequently completed.‌
   • Recovery depended on coordination across teams with different responsibilities and authority, which exponentially slowed resolution.
   • Our initial public updates described an upstream provider outage without clearly distinguishing the specific nature of the interruption. That wording did not adequately explain why Letterhead delivery was affected while the provider's broader service remained available. We apologize for the lack of clarity.

   Corrective actions

   Improve customer visibility into send progress

   Status: In Progress. Target: September 30, 2026.

   ‌We are preparing more granular customer-facing visibility into the stages of a send, distinguishing progress through Letterhead's systems from subsequent provider processing and delivery. Customers will be better able to understand whether a send is progressing, delayed, or incomplete.

   This work was planned before the incident. It addresses visibility into delivery progress.

   Additional provider notifications

   Status: Request acknowledged by provider.

   We have requested additional communication layers and channels for technical and compliance needs, to avoid accidental restrictions. The acknowledgement does not establish that the notification process has been tested.

Reported by Letterhead on their status page.