From John Aylmer (John@Aylmer.com.au):
Mail to external Internet domains accumulates in the Domino server's mail.box. The problem is that although Windows can resolve DNS, Domino cannot. This happens only with some Domino R5 & Windows 2000 installations. You get no error indications anywhere. It looks like a DNS problem but Windows can resolve DNS including making
To prove it is this problem, add the following parameters to your server's NOTES.INI file and restart the Domino server:
One workaround in IBM's KBase is to specify the DNS server's IP directly in the registry. The disadvantage of entering this registry information is that obvious problems will result if the IP's of the DNS servers ever change and the registry edit was not clearly documented. This entry is normally blank even for machines that work OK:
In the data field of the NameServer key enter the IP's of the DNS Servers:
eg. 188.8.131.52, 184.108.40.206
The other fix you could use would be to use an SMTP relay server, DNS resolution is not required if you do this.