Note: This solution only applies to Dimensions MAPI e-mail configuration.
First thing to check is to confirm the correct MAPI e-mail related settings in Dimensions.
If you are running Dimensions via a remote or virtual desktop, then, if possible try running Dimensions installed directly on the user’s PC to see if they have the same issue.
If it works with Dimensions installed on a PC, then it points to the issue being with the way the remote / virtual machine/profile has been configured.
If you also use Access Office Integration (AOI), it is also worth checking the AOI configuration/registration by using the AOI Administrator application. If you get any errors shown in the AOI administration application you may need to re-register the AOI application licence.