It's been awhile, but several months ago, we setup a SBS 2003 with Exchange.\nWe had all kinds of problems with getting mail to go out using SMTP. We\ntried all kinds of setting changes on the server, with our ISP, etc., etc.\nThe people here on this forum suggested all kinds of things that we could be\ndoing wrong with Exchange and our mail setup, but nothing worked.\n\nSo, we had to "bite the bullet" and make a paid call to Microsoft support.\nAfter several days and hours of phone support, we found that the 2Wire\n2700HG-B DSL modem/router supplied by AT&T/SBC has this problem:\n\n[URL]http://support.microsoft.com/kb/314825/en-us[/URL]\n\nBasically, the router does not respond correctly when it gets too large of a\npacket to send. Instead of responding back that the packet needs to be\nbroken up into smaller fragments, the transmission times out and the packet\ngets dropped.\n\nFor a work-around, we did method 1 in the above article to our SBS, but that\ndidn't work. AT&T was not able to provide any further help, so we couldn't\ndo method 2. Method 3 ultimately fixed the issue.\n\nLooking back upon things, other symptoms that had occurred before the\nimplementation of the Exchange server is that we at first were only using\nthe SBS as a DHCP server and gateway. When clients on the network tried to\nsend mail through Outlook and the ISP's SMTP server, we had similar problems\nwhere mail was not going out due to the router dropping large packets and\nnot responding back with the appropriate response.\n\nHope this might help other people, especially with this 2Wire modem/router\nbeing so popular.\n\nThanks to everyone for their help!