Syntax error, command unrecognized error while sending emails

When I send an email from this email id notifier@amritaphr.com, I receive the following error.

Unsent recipients: [receipient's email address here]

INFO 02:33:30,309 | james.mailetcontext | Temporary exception delivering mail (Mail1512206580778-eff844e9-431b-47b1-8dce-3d06bf754dde. RemoteHost said: Send failure (javax.mail.MessagingException: Error issuing SMTP 'DATA' command: CODE = 500 : MSG = mx.zohomail.com Syntax error, command unrecognized: ): org.apache.geronimo.javamail.transport.smtp.SMTPSendFailedException: Send failure (javax.mail.MessagingException: Error issuing SMTP 'DATA' command: CODE = 500 : MSG = mx.zohomail.com Syntax error, command unrecognized: )

at org.apache.geronimo.javamail.transport.smtp.SMTPTransport.sendMessage(SMTPTransport.java:368)

at org.apache.james.transport.mailets.RemoteDelivery.deliver(RemoteDelivery.java:1033)

at org.apache.james.transport.mailets.RemoteDelivery.run(RemoteDelivery.java:791)

at java.lang.Thread.run(Thread.java:745)

Caused by: javax.mail.MessagingException: Error issuing SMTP 'DATA' command: CODE = 500 : MSG = mx.zohomail.com Syntax error, command unrecognized:

at org.apache.geronimo.javamail.transport.smtp.SMTPConnection.sendData(SMTPConnection.java:513)

at org.apache.geronimo.javamail.transport.smtp.SMTPTransport.sendMessage(SMTPTransport.java:349)

... 3 more

My configuration is as follows:

<sslEnable>false</sslEnable>

<gatewayUsername> notifier@amritaphr.com</gatewayUsername>

<gatewayPassword>something</gatewayPassword>

Please help me resolve this issue, as most of the mails are bouncing back with this error.