A syntax error is likely a sign that the email address that the task is sending to, is not formatted properly. The Event Log will tell you what the incorrectly formatted email address is and you will then need to find and update this accordingly.
To update the email address,
check the SMTP (email) step and see it is listed in the "To", "CC" or "BCC" boxes. If the emailaddress is here, update it accordingly.
If the"To", "CC" and "BCC" boxes instead contains code such as'{=ThisStep.DocumentSource.RecordSet' - this indicates that the email address being used is held in the task itself (usually from a view in the associated software, such as FocalPoint). If that is the case, you will need to look at the Database Query (ODBC) step of the task and establish where the email address is held in the associated software - if you need help with this, please log a new case online and reference this article.
Once you know where the email address is held, you can update it as required