2. The Outbox in the Apple Mail app contains the failed
emails when they were sent from your email account.
The mail stuck in Mac outbox is a common problem
in most of the email clients, but it can be fixed using the
below-mentioned steps.
3. Solution:
Step 1:First, check whether you have a stable Internet connection on your Mac device.
Step 2:The internet connection error might probably be one of the reasons for the sent email
failure on your Mac.
Step 3:Click the Apple menu and select the System Preferences option from the drop-down
menu.
Step 4:Click the Network icon and go to the left-side panel.
Step 5:Check whether you have a green light under Wi-Fi or Ethernet.
4. Solution:
Step 6:If the connection indicator light is red, check the connectivity of the Wi-Fi router and the
modem.
Step 7:In the Network window, select the connection medium and click the DNS tab.
Step 8:Configure the appropriate IPv4 or IPv6 address and ports.
Step 9:If the mail stuck in Mac outbox problem persists, contact your ISP to fix the Internet error.