This issue has been verified as resolved as Postfix is no-longer going to be running at all.
We'll be keeping a close eye on the server for the next few hours, though.
Jan 7, 09:37 UTC
Service appears to be running at normal speeds again. Still monitoring closely.
Jan 7, 09:31 UTC
We've set up a fix and deactivated the unused Postfix instance.
We've removed the unneeded logs. We'll be monitoring the service status regarding this issue closely.
Jan 7, 09:27 UTC
We've traced this issue back to Postfix. This is also related to our previous drive-filling issue.
More info to come.
Jan 7, 09:24 UTC