Question About Posts' notifications/e-mail for users in a category ...

I have changed the e-mail for one that is not use in any other user's account.
The problem remains the same.
Notification of a new post is only sent (twice) to this new address, but not to the user who created the topic nor to the one who replied.
I am stuck with this problem.
I join again the Configuration report if you ever need it for trying to find from where comes this problem :

Database collation check: The collation of your table fields are correct
        

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This message contains confidential information

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Kunena menu details:

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ID	Name	Menutype	Link	Path	In trash
483	Forum	kunenamenu	view=home&defaultmenu=485	forum	No
484	Index	kunenamenu	view=category&layout=list	forum/index	No
485	Sujets récents	kunenamenu	view=topics&mode=replies	forum/recent	No
486	Sujets Non Lu	kunenamenu	view=topics&layout=unread	forum/unread	No
487	Nouveau Sujet	kunenamenu	view=topic&layout=create	forum/newtopic	No
488	Pas de réponse	kunenamenu	view=topics&mode=noreplies	forum/noreplies	No
489	Mes Sujets	kunenamenu	view=topics&layout=user&mode=default	forum/mylatest	No
490	Mon Profil (Forum)	kunenamenu	view=user	forum/profile	No
491	Aide	kunenamenu	view=misc	forum/help	No
492	Recherche	kunenamenu	view=search	forum/search	No
493	Forum	mainmenu	Itemid=483	kunena-2022-10-18	No
503	Kunena	mainmenu	view=home&defaultmenu=484	kunena-2022-10-18/kunena	No

Joomla default template details : shaper_helixultimate | author: | version: 2.0.11 | creationdate: Feb 2018

Kunena default template details : Aurelia | author: Kunena Team | version: 6.0.4 | creationdate: 2022-10-30

Kunena template params:

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DefaultCategoryicon
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Kunena version detailed: Kunena 6.0.4 | 2022-10-30 [ Git Repository ]
        | Kunena detailed configuration:

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Kunena config settings:
boardOffline	0
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| Kunena integration settings:

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Kunena - Finder Disabled
 Kunena - AltaUserPoints Disabled
 Kunena - Community Builder Enabled:  access=1  login=1  activity=1  avatar=1  profile=1  private=1  
 Kunena - Easyblog Disabled
 Kunena - Easyprofile Disabled
 Kunena - Easysocial Disabled
 Kunena - Gravatar Disabled
 Kunena - JomSocial Disabled
 Kunena - Joomla Enabled:  access=1  login=1  
 Kunena - Kunena Enabled:  avatar=1  profile=1  

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Joomla! languages installed:
en-GB	English (United Kingdom)
fr-FR	French (fr-FR)

Third-party components: None

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Modules: None

Your mail settings are correct. Remove the mail address again and test whether the users receive the subscription mails with "E-mail to Multiple Recipients = 0". But please check the spam folders first, maybe the mails can be found there.