Throtling in Exchange 2003 - HELP

Hi,

I know that Exchange 2003 is almost out of support but I have one and I need some help about limiting connection.

If anyone can help me I appreciate.

I have an application (LOB) that send emails through Exchange Server 2003 but I intend to limit his connection to avoid queuing emails problem conflicting with users emails.

How can I do that?

Thanks in advance.

Luiz