This is still reproducible on 20211213 nightly build.

Our demo instance of SOGo is not synced with the latest nightly build. Please test in your environment.

That's what I did.

Some users who had vacation auto reply enabled in the past can save the preferences now. Users without existing vacation auto reply preferences still can't. The "Add default email addresses" button is broken for these, too.

Hi Francis,
i am having exactly the same issues as rschuetz - it's working for users with settings changed in the past but not for others that never changed anything. Just installed 5.3.0.20211214 and the issue remains. it's also not working when using sogo-tool to change any of the settings, no error but also no changes
example, here is no error reported, but the settings are not applied:

sogo-tool -v user-preferences set defaults user@domain SOGOMailComposeWindow '{"SOGoMailComposeWindow":"inline"}'
<0x0x5571b3b932a0[SOGoCache]> Cache cleanup interval set every 300.000000 seconds
<0x0x5571b3b932a0[SOGoCache]> Using host(s) 'localhost' as server(s)

Regards Peter

The "Add default email addresses" button still does not work properly for users without existing vacation auto reply preferences. If the prepopulated email addresses are removed from the field they can't be added back by clicking the button. I tracked this down to Preferences.service.js:

if ((angular.isUndefined(data.Vacation.autoReplyEmailAddresses) ||
    data.Vacation.autoReplyEmailAddresses.length == 0) &&
    angular.isDefined(window.defaultEmailAddresses))
data.Vacation.autoReplyEmailAddresses = window.defaultEmailAddresses;

window.defaultEmailAddresses should probably be copied here.