If the user's email settings are set to use MAPI when the system is actually using SMTP, this error will occur.
In such a case, setting the e-mail setup to SMTP resolves the issue. Set the user for SMTP email in Dimensions as follows:
Ribbon style menus:
Click on System
Click on User Records
Select the relevant user
Click Options
Click Edit
Under E-mail Setup, select SMTP
Click Save
Module Menu/Classic style menus:
Click on System Control
Click on User, User Records
Select the relevant user
Click Options
Click Edit
Under E-mail Setup, select SMTP
Click Save
If the system is set to use MAPI, then ensure the user record has an email address and profile configured under the email settings for the user as per this article.