Perform the troubleshooting steps in this article if you send forms, reports, invoices, or other transactions via email through QuickBooks and you keep receiving a message that your email or password is incorrect.
These steps are applicable if you are using Gmail or Yahoo! Mail providers, or if you use the RightNetworks server. If you need assistance in setting up other Web Mail accounts, please see Set up your email service in QuickBooks Desktop.
Gmail may be blocking sign-in attempts to your Google Account. You will have to enable access for less secure apps and turn off 2-step verification for QuickBooks to have the right permissions to send emails using your Gmail account.
Yahoo! Mail has recently implemented a 2-step verification process. This process generates a random password that must be entered into QuickBooks Desktop when it prompts for a password when sending emails. You may also allow access for less secure apps.
AOL has required you to generate and use an app password if you were going to access it via third-party email app and uses 2 - step verification to avoid getting an error.
Check with the developer of your anti-virus for instructions on how to allow communication through these ports.
If you are using McAfee