Which version of quickbooks do you have? Do you get any error while sending email.
Please check if you have already setup your email.
Go to Edit/Preferances/Send forms/Select the appropriate option.
Resolution for 'appropriate option issue: 'Cannot log in to send e-mail invoices' available: Yes.
The appropriate option issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the appropriate option issue yourself by looking for a resolution described in the article. If it is a complex appropriate option issue or you are unable to solve the issue, you may contact us by clicking here or by using other appropriate option support options.
For more information about resolving issues related to appropriate option in Quickbooks/QBO or to get support for the issue 'Cannot log in to send e-mail invoices', click the link below: