Thanks for the clarification regarding "Android 5.0 priority notifications" - I really tried to wrap my head around the possibility of missing out the right combination of enabled options regarding my problem!
Sorry if it was mistakeable:
Enabling "priority senders" alone does nothing (no reaction to a priority senders email adress).
Only enabling "overall notifications" (general options) brings up notifications - but for all / new unread mails and not the priority senders alone.
....
Wait...!
...while writing on this reply I think I found the answer playing and testing around!
So for everyone with the same problem, please try this before you contact support or the forum (forgive me - translating this from the german version):
FIRST
- In the general options -> activate "priority notifications"
- There
- check the first entry "priority notifications"
- add relevant e-mail-adresses
- configure the way you want to be notified (Sound, LED, Vibration, etc.)
-> No need to activate "mail notifications" here, if you want to be informed by mails from special adresses only (if activated it will inform you of ALL new / unread e-mails)!
THEN!
- go to the "special options" for your mail account (one entry above the general options) named "manage accounts"
- choose the relevant account
- go to "special account settings"
- go to "mail notifications"
- There
- enable "special options"
- check "mail notifications"
- DON'T check sound, LED, vibration, etc. (because this will notify you for ALL / NEW unread mails)
- BUT check "notifications with high priority"!
So this combination allowed me to get specified notifications only for mails from my senderadress I used for testing and not from other accounts.
Hope this helps anybody else - thanks nontheless to Kostya for his excellent support and patience.
Best whishes to everyone...
Wolf