To add to what Mariano mentioned, if using Exchange emailing in Dynamics GP, you must be on a minimum of the Oct 2021 release but recommended 18.4, most current release, and be using the new Modern Authentication configuration by Oct. 1st, 2022.
On that date, basic authentication will be permanently disabled by O365/Exchange Online, so if using those with your Exchange emailing in Dynamics GP, the emailing authentication will no longer work without this new Modern Authentication configuration.
The only other option would be to begin using MAPI, which would require a 32-bit email application/Outlook.
For more information, we have numerous blogs and documentation about this or you can ask here.
Thank you,