I cannot send email on my new Mac air. I can receive it fine but cannot send.

Hi there Taz729,

If you can't send email on your Mac, start with the steps below to see if they resolve the issue for you:

* Make sure the outgoing (SMTP) mail server is specified as directed by the provider of your email account. See Verify an email account’s outgoing server.

* Choose Window > Connection Doctor, then follow the instructions displayed in the Details column.

* If there’s a firewall problem, verify that firewall software isn’t blocking email traffic on port 25, 465, or 587. Also check whether you’re affected by another firewall, such as software installed separately from macOS or built into an internet sharing router, or administered by your email account provider. Contact the appropriate person for information.

You'll find this information here: If you can’t send emails in Mail on Mac - Apple Support

If the issue is server-related as you described, you'll want to check your email server settings by entering your email address here: Mail - Official Apple Support

Afterwards, verify your account's server settings with these steps:

1. In the Mail app  on your Mac, choose Mail > Settings, click Accounts, then select an account.

2. Click Server Settings, click the outgoing Account pop-up menu, then choose Edit SMTP Server List.

3. Review information for the server; change settings as directed by your email account provider. 

4. Don’t remove a server that’s in use by an account unless you’re ready to add a different server for the account.

5. Test any changes you made by sending yourself a message.

These steps can be found in this support article: Verify an email account’s outgoing server in Mail on Mac - Apple Support

Take care.