Does anybody know the accepted \ default behaviour of SMTP clients in the following scenario: "A MX record mail.somedomain.com points to 80.80.80.80, the public IP address is changed to 90.90.90.90 and the related MX record is updated. Meanwhile, during the DNS propogation, some SMTP clients will be resolving mail.somedomain.com to 80.80.80.80 still, and there is not active SMTP server found here." The SMTP client MUST retry the message at least once, when a retry is attempted, does the SMTP clint do a further lookup on mail.somedomain.com or will it used some kind of caching mechanism where 80.80.80.80 is stored to avoid overhead? This might sound like a stupid question, but I'm interested to know as I'm a bit confused about EXACTLY how SMTP deals with failure conditions. Thanks Shaun

Start here and follow links for your homework assignment: http://en.wikipedia.org/wiki/Smtp

Um...homework assignment? This isn't for homework, I've done all the academic study I want to for now...10 years of it! I'm trying to understand the underlying behaviour of SMTP, but thanks for your cynical reply anyway, I'll take a look at that link Shaun

Actually, re-reading my initial question I can see how you thought it was a homework assignment, maybe I should get a career in writing assignment questions?! Shaun