After installing and enabling Synology Mail Station (RoundCube), I added a POP3 external account, so that account’s mail also was available at RoundCube’s interface on my Synology.
The issue is that after that change/configuration the NAS didn’t hibernate any more.
I thought that the issue was related to the pooling interval to the POP3 account, and I was right, it was set to 5 minutes by default. I’ve changed to 4 hour’s (240 minutes), but checking the logs I could see that the pooling was still at 5 minutes… and still the NAS wouldn’t hibernate.
So a quick check I’ve found out that the fetchmail process that fetchs the mail from the external POP3 accounts reads it’s configuration files from /var/packages/MailStation/target/roundcubemail/ext
In my case the POP3 account was defined on the admin accounts, and so there is an admin_fetch file, which might be different if other users are using the POP3 external accounts feature.
Editing this file there is a line
#### .fetchmailrc set daemon 300
Which means pooling every 5 minutes (300 seconds)
I’ve changed the value to 21600 (6 hours), and waited for the next NAS restart.
After that pooling was set to every 6 hours and the NAS does hibernate now.
Didn’t bother to much to see how to restart the fetchmail process without rebooting the NAS, but probably restarting the Mail Station packages will suffice.