We use an in house developed PHP based mailing software that connects with Postfix mail server to send out emails through SMTP relay. Every thing had been working fine before but recently we upgraded the mailing software from a single threaded operation to multi threaded one and we started facing SMTP connection failed errors due to timeout. The particular thing about this is that it's an intermittent issue, some times the mail goes through an email address and at other instances it fails. We have tried increasing the process limits in Postfix to see it that helps but to no avail. Can any one please help and suggest some thing.