CloseMenu() also closes the Blizzard MailFrame. SendMail() requires an open MailFrame. Therefore CloseMenu() must NOT be called before mail input.
EditBox OnEnterPressed does not fire when SetScript("OnKeyDown") is set. Enter must be intercepted manually in the OnKeyDown handler.
SkuOptionsEditBoxOkScript is a local variable in SkuZOptions/Core.lua and cannot be called from other files (e.g. mail.lua). Callbacks must be defined as local functions in the calling scope.
RegisterForClicks("AnyDown") prevents double-enter but blocks EditBox OnEnterPressed (fires on key-up). Solution: OnKeyDown handler on EditBox intercepts Enter directly — independent of SecureActionButton override binding.
Debounce approach (100ms lock in PostClick) works for bags and wishlist but breaks mailbox and other EditBox inputs.