This error can be produced for two reasons and there are two sections of steps below to resolve each cause:
When the email address in the Copy E-mail to field in the User Record is an incorrect email format.
The User name of the SMTP Server User Credentials is incorrect.
Copy E-Mail User Record settings
Checking and correcting the content of the Copy E-mail to field can be done as follows. This will need to be done by a user with permissions to edit User Records.
Ribbon style menu:
On the System tab, click User Records.
Locate and select the relevant user’s record.
In the menu bar, click the Options icon. The Options window appears.
In the E-mail Setup field, check that the user has SMTP set. If it says MAPI, then refer to the article about this error for MAPI only.
To close the Options window, click the red X icon.
In the menu bar, click the Email icon.
Check there is a tick in the Copy E-mail to box with a text box besides it.
Edit the email address in the Copy E-mail to text box to ensure it is a valid email address.
Click OK (disk icon).
To close the User Records window, click the red X.
Module Menu / Classic style menu:
Select System Control from the navigation bar
Click on Users, then User Records
Scroll to locate the relevant user’s record and click on the row to highlight it
Click on the Options icon in the menu bar to display the Options window
Check that the user has SMTP set in the E-mail Setup field. If it says MAPI, then this article is not applicable.
Click on the red X icon to close the Options window
Click on the Email Details icon in the menu bar
There should be a tick in the Copy E-mail to box with a text box besides it
Edit the email address in the Copy E-mail to text box to ensure it is a valid email address
Click on the OK button (disk icon)
Click on the red X to close the User Records window
SMTP Server User Credentials
To check and revise the SMTP Server User Credentials, do the following:
Ribbon style menu:
On the System tab, click Options, System Control Options.
On the System Format tab, next to System E-mail Defaults, click the blue arrow.
Click the SMTP Users icon.
Check the value in the User name field and ensure it is set to a correct user account for accessing the SMTP e-mail server.
Module Menu / Classic style menu:
Select System Control from the navigation bar
Click on Options, System Options
Click on the System Format tab
Click on the blue arrow next to System E-mail Defaults
Click on the SMTP Users icon
Check the value in the User name field and ensure it is set to a correct user account for accessing the SMTP e-mail server.
This issue can also be caused by Windows Updates.
Find when it last worked, and then uninstall and windows feature updates from after that time, restart, and try again. (Don't worry, the next time you check for updates Windows will reinstall what was removed)
To do this:
Open the start menu and type Windows Updates
Click View Update History
Click Uninstall Updates
In the Microsoft Windows section of the updates list, Uninstall any updates from after the last time emailing was working
Restart the machine and try emailing again