smtp sending error

[tekKnoXpresso]

I'm using a email marketing program to send mass emails. I want to use my zimbra server to send the emails. I input my server address for the smtp and test the connection and it's able to connect fine. When I try to send the emails it fails and here is the error it gives me.

Successfully connected to SMTP Server

txxxxx@axxxxxxv.com - Failure - EMPLog:
SendEmail:
DllDate: Jan 10 2008
Username: tjk
Component: .NET 1.*
Using existing/open SMTP connection to send email.
subject: test2
reversePath: elliotxxxxxx@elliotxxxxxx.com
recipients:
554 5.7.1 <txxxxxx@axxxxxv.com>: Relay access denied
Failed when sending RCPT TO:<txxxxxxk@axxxxv.com>
bad_address: txxxxxx@axxxxv.com
NumSuccess: 0
NumTotal: 1
Send failed.
tekknoxxxx@gmail.com - Failure - EMPLog:
SendEmail:
DllDate: Jan 10 2008
Username: tjk
Component: .NET 1.*
Using existing/open SMTP connection to send email.
subject: test2
reversePath: elliotxxxxxxx@elliotxxxxxx.com
recipients:
554 5.7.1 <tekknoxxxx@gmail.com>: Relay access denied
Failed when sending RCPT TO:<tekknoxx@gmail.com>
bad_address: tekknoxxxxx@gmail.com
NumSuccess: 0
NumTotal: 1
Send failed.
Email Marketing Pro has completed transmitting 2 messages. 0 messages were sent successfully and 2 message deliveries failed.

I've tried other programs like outlook to send my emails but I'm still not able to send any.