Toward the end of 2022, Microsoft made some changes that affect users who want to send email from RTG Bills or RTG Bills Online using the Microsoft email server.

RTG Bills and RTG Bills Online require that you sign in to the Microsoft email server with a username and password. Microsoft calls this SMTP AUTH.

Microsoft explains how to allow SMTP AUTH here:

Enable or disable authenticated client SMTP submission (SMTP AUTH) in Exchange Online

IMPORTANT NOTE:
Normally, you can turn off SMTP AUTH for your organization but turn it on for a specific mailbox. However, as noted on the page linked above, Microsoft offers a feature called security defaults that disables SMTP AUTH for all mailboxes and it does not allow exceptions. Microsoft says: "To use SMTP AUTH, you need to disable security defaults." They provide a link for further information.

Use these email settings for RTG Bills Online:

SMTP Server: smtp.office365.com
SMTP Port: 587
Server requires authentication
Use SSL or TLS: TLS

Use these email settings for RTG Bills on a PC:

SMTP Server: smtp.office365.com
SMTP Port*: 5870
Server Requires Authentication

*Note: 5870 is a code that tells RTG Bills to use port 587 and the STARTTLS encryption protocol.

In addition, you need to install the update from this page:

RTG Bills Email Update