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If you're not the technical contact, it's reasonably likely that you don't have the authorizations necessary to make significant configuration changes. The needed changes are probably needed to either your e-mail server or your internet servers (e.g., DNS server for mail routing probably controlled by your service provider).
You need a qualified person to make such changes or to coordinate them with a provider. The probable help really isn't a good idea through a forum. This forum is intended to work with qualified technicians. The amount of information needed would approach the scale of a training course. It simply isn't feasible.