It seems that on some computer the links failed. If we add rel="noreferrer" on tag <a> then it works fine.
So we should have
<a class="user-infos-mail-title exchange-user-infos-mail-title" href="https://owa.xxxx.fr/owa" rel="noreferrer" target="_blank">Messagerie :</a> et <a class="user-infos-agenda-title exchange-user-infos-agenda-title" href="https://owa.xxxx.fr/owa/#path=/calendar" rel="noreferrer" target="_blank">Prochain(s) RDV :</a>