Gmail has instituted new security measures for sending emails via Printer, Fax or third party Applications. This setting can prevent emails from being sent through Theatre Manager even when the SMTP server settings are added correctly. Any clients using Gmail for sending outgoing email should be aware of these settings.
It seems any application that is not a Google product is deemed a less secure app when using Gmail SMTP servers. This does not mean the application, in this case Theatre Manager, poses a security risk. It simple means Google is attempting to protect itself should the SMTP details be used in an incorrect manner. For more information on how Google perceives other applications please see the details in the article.
When using Gmail as an outgoing SMTP provider suddenly emails stop sending. The Pending/Unsent emails list indicates the Password is wrong. When checking the Web Server settings in Company Preferences the password has been typed correctly but the emails still fail with a "Bad Password" error.
By altering the setting you should now be able to send outgoing email using Gmail again.
Gmail will send an email indicating the setting has been changed. This email suggests changing the setting may lead to security issues. This is the only way to ensure outgoing email will not be blocked when using Gmail SMTP settings.