501 5.5.2 RCPT TO syntax error
The destination email address is invalid according to the RFC 2822 Internet message format standard.
Some systems allow addresses that are not fully compliant with the standard.
A typical example is an email address whose local-part begins or ends with a ‘.’ (dot, period or full stop) character. This is not allowed by the standard. Some receivers may, however, choose to accept these addresses by ignoring the additional character, or using it as a component of the unique local-part.
SmartRelay enforces the standard and refuses to accept an email sent to an invalid address. This behavior can, however, be changed if required.
This is a permanent error. Re-sending the message will not succeed unless the recipient address is corrected.