mail.alga.pl has one IP number , but no corresponding reverse pointer. psew.pl, pwea.pl, myinet.pl, psew.org.pl, mail.bic.pl and at least 100 other hosts point to the same IP. alga.pl use this as a mailserver. alga.pl is a domain controlled by two nameservers at inet.pl. They are on the same IP network. Incoming mail for alga.pl is handled by one mailserver at alga.pl themselves. alga.pl has one IP number. mail.alga.pl is hosted on a server in Poland.