SUMMARY
When I added a new IMAP folder I wanted to set the expire date for "Expire unread messages after" to 90 days. After saving the value and checking again, I suddenly had a value of 21926 days. Checking my other folders this wrong value was set, too - at least something near it, like 22034 or so. There seems to be another problem with the expire settings - the folder where expired messsages should be stored are gone after saving the value, too.

STEPS TO REPRODUCE
1. Set a New "Expire unread messages after"-Date (I think more than 30 days)
2. Save
3. Check the value again

OBSERVED RESULT

A ridiculous value, around 22000 days.

EXPECTED RESULT

The value I entered

SOFTWARE/OS VERSIONS

Linux/KDE Plasma: 5.16.5
(available in About System)
KDE Plasma Version: 5.16.5
KDE Frameworks Version: 5.62.0
Qt Version: 5.12.5

ADDITIONAL INFORMATION