Resolving issues with emails sent to multiple recipients in Outlook for Exchange can be done in the following steps:

1. Verify SMTP settings: Check mail server settings to make sure you have accurate SMTP settings.
2. Restart mail services: Restart the mail services on the server to ensure that it is up and running.
3. Check firewall settings: Verify firewall settings to make sure it is not blocking outgoing emails.
4. Review mail server logs: Check mail server logs to determine if there are any errors or warnings that could be causing the issue.
5. Review Exchange permissions: Check the Exchange permissions to make sure the user has the correct permissions to send emails to multiple recipients.