Lindsay Haisley writes:
Just so I have this straight, would someone check me out on this procedure. What I want to do is move the destination for a bunch domain names from one machine - machine A - to another on a different network - machine B. After the move, I want any residual mail in the Internet mail system delivered to machine A due to cached DNS info to be redirected to machine B by machine A.Currently machine A is the preferred MX server in DNS-space. Using webadmin, I have all the domains for which A accepts mail listed under "Locally-hosted Domains" on A, which causes them to be listed in /etc/courier/esmtpacceptmailfor.dir/webadmin, and hence, I assume in the database in /etc/courier/esmtpacceptmailfor.dat. Mailboxes for each domain are supported by a MySQL database which references a mailbox, or possibly a .courier file in an alias directory. My reading of the documentation indicates that to switch to another server I need to do only the following: 1. Set up machine B in DNS-land as the low number (preferred) MX for each such domain name for which I want mail relayed. 2. Make sure that mail to each mailbox or alias in said domain on machine B is deliverable locally, just as it had been previously on machine A. Do I need to disable delivery on machine A so that mail to those mailboxes for which it previously accepted delivery are no longer available, or will Courier simply look at the MX records, note (on box A) that it's no longer the preferred MX, and automatically requeue it for delivery to machine B?
You have reconfigure the domain as a non-local domain. Remove it from hosteddomains, but keep in esmtpacceptmailfor.
First, define the other server as the preferred MX in DNS, and let the DNS changes propagate as far as your own machines are concerned.
I do not believe that webadmin implements this kind of configuration, so you'll have to do it manually. Stop incoming SMTP, so you do not interfere with normal mail flow while you're doing all this. Remove this domain as a locally-hosted domain, in webadmin. Before you actually install the webadmin configuration, put the domain into some different file in esmtpacceptmailfor.dir
Once you install the configuration via webadmin, all the config changes should take effect immediately, and you can reenable SMTP.
Courier must recognize this domain as a non-local domain, so its mail gets delivered remotely. Courier should see itself as a less-preferred MX for this domain, and attempt to deliver the mail only to the preferred MX.
In rare situation Courier cannot figure this out. Courier tries to match the hostnames in DNS MX records with its known list of local hostnames. Whatever your machine A's name is defined in DNS, it must be one of the local domain names. Note, that means that your MX record must use a different hostname. You cannot do something like:
example.com. MX 10 example.com. example.com. IN A 192.168.0.2If example.com is listed in locals, mail to that domain gets handled as local mail.
As long as your DNS config is sane, and matches Courier's config, forwarding should work automatically. In extreme cases you can always fallback on an explicit setting in esmtproutes.
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