The value for the RCPTRESPONSEDELAY statement must be positive. This statement specifies how long the SMTP server delays responding to the RCPT commands from the sender SMTP. While it is waiting for domain name resolution. If resolution does not complete before the specified period, the SMTP server assumes name resolution is successful and sends a reply code of 250 ok. to the sender SMTP and queues the recipient address for asynchronous resolution. If the name resolution is later determined to be unresolved, the mail is returned to the sender. SMTP uses the default value for the RCPTRESPONSEDELAY statement, which is 60 seconds. For more information on this statement, see the z/OS Communications Server: IP Configuration Reference.