For the very first try of your online store made in Zen Cart, I am sure you will encounter this error:
This happens when a user tried to register on your store. In order to fix this kind of error, you should change the settings in the Zen Cart’s Admin area. So first log in your store’s admin area like shown in the image below:
From here you must change the Email Transport method:
Click the row and change the settings on the right side of your screen. Servers running on Windows and MacOS should change this setting to SMTP.
The setting will depend on your e-mail server and other options. If you have your own e-mail server, you must choose the SMTP
or SMTPAUTH.
There are 4 important parameters when using SMTP or SMTPAUTH. You have to include your account mailbox, account password, the mail host, and the mail server port (which is usually port 25).
When you have change these settings, most likely, your users will be able to register on and purchase items on your online store.
Hope this post helps! Thank you for reading my article! 
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