The main cause is either missing or incorrect login details—especially your username and password for the outgoing mail server. Other possible reasons include using the wrong SMTP port number or problems with the Mail app settings after an iOS or macOS update. Now that you know the causes, let’s discuss the solutions.

1. Set a Custom DNS on Your Mac

This method should fix the issue as long as you don’t change your Mac’s network settings later, and as long as BT doesn’t deactivate the DNS servers you add.

2. Change the Hostname on Your Router

This is another possible fix. This will work for your Mac on this specific router. If you connect to a different BT Hub, you’ll need to repeat this process.

3. Change the Name of Your Mac

Since this issue often comes from the Mac’s hostname, using a name with no spaces or symbols can help you connect anywhere.

Fix Apple Mail and BT Internet Won t Send Emails - 81Fix Apple Mail and BT Internet Won t Send Emails - 86Fix Apple Mail and BT Internet Won t Send Emails - 61Fix Apple Mail and BT Internet Won t Send Emails - 11Fix Apple Mail and BT Internet Won t Send Emails - 59Fix Apple Mail and BT Internet Won t Send Emails - 19Fix Apple Mail and BT Internet Won t Send Emails - 58