how about calling the setting: "receive own emails" with the options "Yes" (i.e. enable sending) or "No" (disable sending)?
Possibly this could be more accurate, but would require much unexpected change to preserve behavior.
Also it his historical : before this parametrer exist, users always received own mails.
And we always preserve existing behavior for existing users, so "not receive own mails" seemed a good option, with default to no.
BTW, the wording with "his" also excludes all female ProjeQtOr users...
You're right, it is an inacurate translation from french to english (our devs are french

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Replaced with "not receive own emails"
Is is possible to set a default value for this option for all users? I'd like to make "not receive his own emails" = "Yes" (disable sending) the default on my installation.
Yes, you'll find same parameter in Global Parameters (tab "Display", section "default values for user paramerters")
Every time a parameter exists as Global and User, Global is default value for new users.