On August 21st 2020 at 07:33 UTC our US1 mail relay server experienced a delay while sending emails. The issue lasted for approximately 3 hours.
This issues was caused by a pending abuse notification that was not acted on in time. The abuse notification originated from an e-mail recipient at one of our customers. The customer had not set their SPF record correctly, causing their outgoing e-mails to be marked as spam by the recipient.
To prevent this issue we took several actions to ensure that abuse notifications are directly visible to our SaaS team. We also contacted the customer to make sure they set their SPF record correctly.