postfix relay error Host or domain name not found.
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Can I relay through Grande's mail server from my friends house or my office?
Yes, however you will need to CHECK your mail first. After a successful mail check, the IP address of the remote location that you are coming from will be permitted to send mail for a period of 30 minutes. Each new successful POP3 check will extend your permitted relay period for a new 30 minutes.
Well I suppose that is possible, but then you shouldn't be able to telnet in and send a message from that machine. Even then the error says it can't find the domain. That smacks of a DNS issue. What happens if you enter the IP address instead of the hostname.
You are restarting postfix after each change right? I don't think I explicitly said to restart postfix but you muse do that after editing the config files.
Try it with the IP Address of 18.104.22.168. If that works it is a DNS issue. If that fails, then the problem is either in postfix or your NAT Router, or possibly that your ISP is blocking SMTP traffic, though I would expect different errors if that were the case.
going by ip seems to have worked, recieved the message at my gmail account. although the address shows up @xxxxxx.dyndns.org rather than to actual domain, i think i must have misunderstood the purpose the cname thing.
You can live with this as long as you are sending all your mail through your ISP's server. However, it would be something I would want to resolve because:
a. Your ISP's SMTP Server address could change
b. Postfix should be able to resolve hostnames.
Afraid I am not sure where to start on this one, perhaps a strace or tcpdump could help find the problem.
2. "the address shows up @xxxxxx.dyndns.org"
This one is really only a problem if it is showing up in the 'From' address that way. If it is you need to set postfix and / or your mail client to use your actual domain name.
3. Technically SMTP servers should NOT be set up as a CNAME, but should always point to an 'A' record.
So you should set your MX record to point to 'gandawaco.dyndns.org' (an 'A' record) rather than to 'mail.gandacomputers.com' (a 'CNAME')