Know How to Fix Apple Mail “SMTP Server Not Working” Error

One of the most frustrating situations is when you try to compose an important e-mail, hit send and your message refuses to leave your Outbox folder. Although for the users of Apple devices the standard Apple Mail client is surely an appropriate place to manage different email accounts at once, it tends to display unexpected connection errors such as “SMTP Server Not Working” and “Cannot send message using the server”.

The Simple Mail Transfer Protocol is a protocol that is designed to forward your emails from your computer to your mailbox server and then to the recipient. In case of a problem in this process, you are going to be able to receive your incoming emails (IMAP and POP protocols), but unable to send any messages.

This guide is designed to help you figure out what caused this problem and how to fix it.

Why Does the SMTP Error Occur?

Before we explore solutions, it is important to examine some reasons why SMTP connections fail in macOS:

• Corrupted Server Address Information: A slight error in your outgoing server address, out-of-date port information or inactive SSL settings can make the whole process impossible. 
• Incorrect Password: In case you have just changed the password of your email on the web interface provided by your service provider (Gmail, Outlook, Yahoo, etc.) but haven’t updated it on the list of outgoing servers in Apple Mail, the server will not let you in. 
• Excessive Third-Party Security or a Virtual Private Network (VPN): Excessively strict firewall settings, third-party antivirus software or a virtual private network may block access to the required network ports.
• ISP Port Blocking: Internet Service Providers often block common outgoing ports such as port 25 to avoid spam.

Step 1: Use Apple’s Built-In “Connection Doctor”

Apple Mail comes with a built-in diagnostic tool that is especially geared towards diagnosing connectivity problems.

• Launch the Mail application on your Mac computer.
• From the top bar, select Window > Connection Doctor.
• See the status list. The accounts that are marked with a green tick are operating normally, while the accounts that are marked with a red cross have failed connections.

See the detailed error log from the Connection Doctor panel below.

Step 2: Verify and Correct SMTP Server Settings

Incorrect setup is one of the main reasons for SMTP issues. Maybe your mail service updated its servers, and now your Mac tries to connect to an outdated server address.

Step 1. Launch Mail and open Settings (Preferences).

Step 2. Select the Accounts tab and choose your problem email account from the sidebar.

Step 3. In the Outgoing Mail Server (SMTP), you need to find the drop-down menu.

Step 4. Open the drop-down menu and select Edit SMTP Server List.

Step 5. Select your specific server and check the information in the Advanced tab:

• Port Number: Secure SMTP ports can be 465 or 587. Make sure Use TLS/SSL option is selected.
• Authentication: Set the authentication method as standard (it should be password), enter your username (your full email) and password. Note: although some fields may seem unnecessary, re-adding your credentials will help to establish connection.

Step 6. Now click OK and try to send a test email.

Step 3: Address App-Specific Passwords and Two-Factor Authentication

In case that you are using popular email services like Gmail, Yahoo, or Outlook, access via third-party applications is usually limited without the use of Two-Factor Authentication (2FA) together with an App-Specific Password.

Should you have just set up 2FA for your email account:

• Access your email service account through a web browser (e.g. mail.google.com)
• Go to your account security settings and create a new App-Specific Password specifically for Apple Mail/Mac.
• Access Apple Mail and go to Preferences > Accounts. Select your account and enter the generated token instead of your main account password.

Step 4: Check for VPN and Firewall Interference

But when your settings are correct and you still receive this alert, it can be because of some network security software.

• Deactivate your VPN: Most of the times, some security flags are raised in the mail server by the protocols of the VPN as they pass the traffic through certain servers. Disconnect the VPN and try sending a message from the Outbox of Apple Mail.
• Check the Firewall Settings of macOS: To do this, open the System Settings > Network > Firewall.

Step 5: Deleting and Adding Back the Email Account

In case your preferences are corrupt, the best way to go about solving the problem would be to reset the slate and have macOS create the connection profile anew.

• Head over to System Preferences > Internet Accounts (or go to Mail > Preferences > Accounts).
• Choose the problematic email account and select Delete Account. (This won’t affect your real email on the web server, do not worry).
• Restart your computer to flush any temporary cache files.
• Go back to Internet Accounts, click Add Account and follow through to log in again. This time around, macOS will set up the default settings for you.

Preventing Future Outbox Stalls

In order to avoid future problems associated with SMTP errors, make sure to look up your system status page whenever you run into an error suddenly. Staying current on updates for your macOS will ensure that your email program remains compatible with any security measures.