Hi hilarymarsh,
We understand that you're unable to send mail via your Gmail account on your Mac.
To start, let's check out the Mail Connection Doctor which can offer some additional insight as to what may be happening. To run the Mail Connection Doctor, you can open Mail, choose Window > Connection Doctor from the menu bar. From here, you can select the account and choose Show Detail to gather more information.
You can also reference this article which explains how to troubleshoot Mail on your Mac: If you can’t send or receive email on your Mac - Apple Support
"Test using webmail
Many email providers offer webmail, which is a way to use email with a web browser such as Safari, instead of with an email app such as Mail. For example, if you're using an iCloud Mail account, you can use iCloud.com to send and receive email.
Webmail is a good way to verify that your account is valid, but it doesn't mean that your account is set up correctly in Mail. Your email provider can help you verify your email settings and check for other issues that affect sending or receiving email.
Remove your email account, then add it back
If no other solutions work, follow these steps:
- Remove your email account in Mail.
- Add your email account in Mail again.
- Try to send and receive email."
We hope this helps.
Take care!
