Summary of Impact: Between 15:00 and 22:00 UTC customers may have experienced issues with delayed delivery of emails due to G Suite rejecting connections from Exclaimer Cloud.
Root Cause: Transient rejections were issued by G Suite's SMTP relay service when Exclaimer Cloud attempted to initiate the connection. Exclaimer Cloud will not accept the email from G Suite until we have confirmed we are able to complete the return connection - this ensures that email is always 'owned' by G Suite and never Exclaimer. As we are unable to create the return connection we are in-turn unable to accept the message from G Suite. These emails then sit in G Suite's own queue awaiting retry - this queue has long waits between retries, exacerbating the issue (~5min/15min/40min).
Mitigation: G Suite stopped rejecting sessions and the issue was resolved.
Next Steps: We are working closely with Google and are deploying a number of changes to the way that Exclaimer handles retries and distributes connections for G Suite emails.