
Use SSL to connect to the outgoing mail server in Mail on Mac
If the provider of your email account supports SSL (Secure Sockets Layer, a security technology) for the outgoing (SMTP) mail server, you can ask your provider to supply the information you need to connect to the outgoing mail server using SSL.
- Go to the Mail app  on your Mac. on your Mac.
- Choose Mail > Settings, click Accounts, select an account, then click Server Settings. 
- If necessary, deselect “Automatically manage connection settings.” 
- Select Use TLS/SSL. - The port number is automatically changed; edit the number, if necessary, to match the information supplied by your provider. 
- Click Save, then close Mail settings. 
- Click Save in the message that appears. 
If you receive an “Unable to connect” error message after making the change, deselect Use TLS/SSL and contact your email account provider.