Abstract: A mail server system includes a congestion control management section managing a congestion control over the mail server system, a congestion statistical information collection section collecting the congestion statistical information of each mail server, and a resend queue having enough capacity, wherein a retry server for performing a retry process is provided. The congestion control management section detects the mail server where a fault occurs from the collected congestion statistical information and gives an instruction of regulating the sending of a mail directed to the faulty mail server to each mail server. The mail server instructed the regulating the sending of the mail directed to the faulty mail server transfers all the mails directed to that destination to the retry server, and transfers the received mail directed to the faulty mail server to the retry server until there is a regulation dissolution instruction from the congestion control management section.