New Exchange 2003 server - unable to send external email

[StevieM]

I have an Exchange 2000 server and have just installed an Exchange 2003 server to replace it.

I migrated a few users to the new server this weekend and they seem to be okay, except they cannot send external mail. They send/receive internal and can receive external but when they try to send they get a "5.7.1 smtp;550 5.7.1 Unable to relay for a@b.com" NDR. Users on the original Exch 2000 box are fine.

I have looked at SMTP and DNS and can see nothing obvious, does anyone have any ideas what may be causing it?

Thanks

 

[ntinlin]

Is the new server sending directly using DNS lookup or via a Smart Host on your ISP?
Or should it still be routing via the old server?

More information is required in other words.
Neill

 

[mug10]

Check the MX record

 

[58sniper]

MX record (for the recipient's domain) isn't an issue here if users on the other server can send fine.

Pat Richard
Microsoft Exchange MVP

 

[Zelandakh]

On the Exchange Server 2000 you need to allow the 2003 box to relay through it. This will solve your crisis allowing you to work out why that box needs to relay emails out!

 

[ElderBlack]

if all else fails check firewall settings.
Some Win Servers are arriving in an almost total lock down and you need to open the connections to send or recieve information.