To all selected - a letter is sent to all users who meet a specified rule.
To addresses that certainly exist - an address is considered as a certainly existent one if at least one letter was sent to it before, and a user viewed this letter.
To addresses where there is a permission for mailings - a letter is sent to users who gave a consent for receiving mailings with the help of Double Opt-In
To decrease a risk of letter falling to spam folder we recommend sending of mailings to addresses where there is a permission (i.e. only for confirmed addresses). Check this article to know what impacts the level of delivering of letters.
Below you can check results of a selection:
Who meets a rule - how many objects meet specified conditions.
With specified email addresses / Addresses that certainly exist / Addresses where there is a permission for mailings - depends on “Send by” option settings.