Hi Fiona @ ERP the best thing to do is to create a custom mailflow connector in Exchange Online that authenticates mail based on an IP range to sidestep basic authentication or modern authentication entirely.  From everything I've read, the retirement of Basic Authentication won't affect custom connectors authenticated by IP.  So you would create a  "Sage 300" mailflow connector and enter the IP range of your RDS servers for Authentication.  If I hear any different I'll let you know.  Hope that helps.

Hi Fiona @ ERP the best thing to do is to create a custom mailflow connector in Exchange Online that authenticates mail based on an IP range to sidestep basic authentication or modern authentication entirely.  From everything I've read, the retirement of Basic Authentication won't affect custom connectors authenticated by IP.  So you would create a  "Sage 300" mailflow connector and enter the IP range of your RDS servers for Authentication.  If I hear any different I'll let you know.  Hope that helps.