Problem replying email

[2Sweet]

A user when replying emails (from MS Outlook 2003) to some of the internet
users, it always undelivered and bounce back (refer to below for the
errors). But when user manually keyin the email address, it sent
successfully. It always happened on these 3 domain email accounts.

The e-mail system was unable to deliver the message, but did not
report a specific reason. Check the address and try again. If it still
fails, contact your system administrator.

<smtp02.nafa.edu.sg #5.0.0 smtp;550 5.0.0 ... Use MXes or
authenticate yourself>





There was a SMTP communication problem with the recipient's email server.
Please contact your system administrator.

<smtp02.nafa.edu.sg #5.5.0 smtp;553 sorry, you must authenticate
and be authorised to use this service (#5.7.1)>





There was a SMTP communication problem with the recipient's
email server. Please contact your system administrator.

<smtp02.nafa.edu.sg #5.5.0 smtp;530 Authentication required>

 

[Brian Tillman]

A user when replying emails (from MS Outlook 2003) to some of the
internet users, it always undelivered and bounce back (refer to below
for the errors). But when user manually keyin the email address, it
sent successfully. It always happened on these 3 domain email
accounts.

Are you using POP/SMTP accounts and do those account definitions
authenticate to the outgoing server?

 

[2Sweet]

Using SMTP account. Problem only when reply to these 3 domain email address.
But when manually type the email address, it sent successfully.

 

[Brian Tillman]

Using SMTP account. Problem only when reply to these 3 domain email
address. But when manually type the email address, it sent
successfully.

You didn't answer all of the question. Are the accounts authenticating to
the outgoing servers?

 

[2Sweet]

the accounts do not require to authenticate to the outgoing server.

 

[Brian Tillman]

the accounts do not require to authenticate to the outgoing server.

The error message you received clearly indicates otherwise.