Hi @Kareem Soliman
I understand your situation. It seems that the welcome email for new members in Microsoft 365 groups is enabled by default, if you want to disable it, try the following command:
Connect-ExchangeOnline Set-UnifiedGroup -Identity "ExampleGroup@contoso.com" -UnifiedGroupWelcomeMessageEnable:$false
Microsoft official document source: https://learn.microsoft.com/en-us/powershell/module/exchange/set-unifiedgroup?view=exchange-ps#-unifiedgroupwelcomemessageenabled.
Hope this helps.
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