Delayed delivery of some emails (affected domains: gmail.com and gmx.de)

This incident has been resolved.

The underlying error has been corrected.

We started to route a small part of outgoing emails back to the affected systems and verified that performance is fine again.

We'll keep monitoring the systems closely as we slowly restore the original setup.

Email delivery works again without any delays since around 10:39 UTC (mitigation applied to last system).

We are monitoring the systems.

We've identified the underlying problem.
The queued/delayed emails are being delivered now.

We've rerouted emails from the impacted part of our sending infrastructure to the not impacted part.
New emails shouldn't be delayed anymore, but queued emails still need to be processed.

We're still looking for the underlying cause of the delay.

A part of the emails for recipients addressed to gmail.com and gmx.de are delivered with a delay. (Emails won't be lost.)

We are currently investigating.