Update #3: rDNS records have been fixed as well. Email traffic will resume normally.
Update #2: IP delegation issue (missing rDNS records) has been assigned to RIPE NCC. They're currently investigating why it is not properly delegating to our name servers. There is no ETA yet.
Update #1: onsite technician has successfully rebooted DEER server. Server went down with "Out of memory" errors. Server has 264 GB of DDR4 of memory, more than enough for any process or task, including backups. Next month we're going to power down server for about 1 hour then then perform memory test (hardware test). We cannot schedule any hardware tests during busy holiday season.
In the meanwhile, we'll monitor memory usage. Once it reach 80%, we'll reboot server to prevent longer downtime. Server reboots normally take less than 3-5 minutes.
We're currently investigating server (DEER) outage in Dallas data center. We've already tried to reboot server remotely, but it didn't come after reboot.
Data center technicians onsite will check server manually. They'll check power cables, network and disks. There is no ETA.
Second issue is related to IP subnet. It was unexpectedly transferred by netblock owner and we lost all rDNS records. As a result, some emails started to bounce back because IPs do not have rDNS records. We'll try to fix this as well with networking team.
Thank you for your patience.