smtp1.byte.nl has one IP number , but the reverse is mx.c1.byte.nl. 75.nu, amx.nl, alo.nu, odp.nl, aadf.nl and at least 100 other hosts use this as a mailserver. byte.nl is a domain controlled by four nameservers. Some of them are on the same IP network. Incoming mail for byte.nl is handled by three mailservers at byte.nl themselves. Two of them are on the same IP network. byte.nl has one IP number. smtp1.byte.nl is hosted on a server in Netherlands.