We have two Domino4.62 and Domino5.03 servers as mail server in our company. Suddenly, 5.03 server can not send mail to the 4.62. The error messgae: Fail to connect to SMTP host (name of 4.62) via SMTP: Server not responding. I did not change anything, it was working fine. 4.62 has no problem to send the mails to 5.03. Tow mail servers have no problem with send mails and receive mails with other mail systems.