The term "RCPT" stands for Recipient, which is the destination email address.

The error indicates that there is an invalid character in the recipient email address. 

The most likely culprit is a leading or trailing space because you cannot see them easily.

NetCommunity trims the spaces from the display view in the report but the email in the Imported list created from a CSV file that the email uses to send from will still retain the space, which causes the error.

- For Imported lists review your CSV file and ensure there are no leading or trailing spaces in the email and re-upload the list to NetCommunity.