28.5. Troubleshooting

28.5.1. Why do I have to use the FQDN for hosts on my site?
28.5.2. Sendmail says mail loops back to myself.
28.5.3. How can I run a mail server on a dial-up PPP host?
28.5.4. Why do I keep getting Relaying Denied errors when sending mail from other hosts?


Why do I have to use the FQDN for hosts on my site?

The host may actually be in a different domain. For example, in order for a host in foo.bar.edu to reach a host called mumble in the bar.edu domain, refer to it by the Fully-Qualified Domain Name FQDN, mumble.bar.edu, instead of just mumble.

This is because the version of BIND which ships with FreeBSD no longer provides default abbreviations for non-FQDNs other than the local domain. An unqualified host such as mumble must either be found as mumble.foo.bar.edu, or it will be searched for in the root domain.

In older versions of BIND, the search continued across mumble.bar.edu, and mumble.edu. RFC 1535 details why this is considered bad practice or even a security hole.

As a good workaround, place the line:

search foo.bar.edu bar.edu

instead of the previous:

domain foo.bar.edu

into /etc/resolv.conf. However, make sure that the search order does not go beyond the boundary between local and public administration, as RFC 1535 calls it.


Sendmail says mail loops back to myself.

This is answered in the Sendmail FAQ as follows. This FAQ is recommended reading when tweaking the mail setup.

I'm getting these error messages: 553 MX list for domain.net points back to relay.domain.net 554 <user@domain.net>... Local configuration error How can I solve this problem? You have asked mail to the domain (e.g., domain.net) to be forwarded to a specific host (in this case, relay.domain.net) by using an MX record, but the relay machine does not recognize itself as domain.net. Add domain.net to /etc/mail/local-host-names [known as /etc/sendmail.cw prior to version 8.10] (if you are using FEATURE(use_cw_file)) or add Cw domain.net to /etc/mail/sendmail.cf.


How can I run a mail server on a dial-up PPP host?

Connect to a FreeBSD mail gateway on the LAN. The PPP connection is non-dedicated.

One way to do this is to get a full-time Internet server to provide secondary MX services for the domain. In this example, the domain is example.com and the ISP has configured example.net to provide secondary MX services to the domain:

example.com. MX 10 example.com. MX 20 example.net.

Only one host should be specified as the final recipient. For Sendmail, add Cw example.com in /etc/mail/sendmail.cf on example.com.

When the sending MTA attempts to deliver mail, it will try to connect to the system, example.com, over the PPP link. This will time out if the destination is offline. The MTA will automatically deliver it to the secondary MX site at the Internet Service Provider (ISP), example.net. The secondary MX site will periodically try to connect to the primary MX host, example.com.

Use something like this as a login script:

#!/bin/sh # Put me in /usr/local/bin/pppmyisp ( sleep 60 ; /usr/sbin/sendmail -q ) & /usr/sbin/ppp -direct pppmyisp

When creating a separate login script for users, instead use sendmail -qRexample.com in the script above. This will force all mail in the queue for example.com to be processed immediately.

A further refinement of the situation can be seen from this example from the FreeBSD Internet service provider's mailing list:

> we provide the secondary MX for a customer. The customer connects to > our services several times a day automatically to get the mails to > his primary MX (We do not call his site when a mail for his domains > arrived). Our sendmail sends the mailqueue every 30 minutes. At the > moment he has to stay 30 minutes online to be sure that all mail is > gone to the primary MX. > > Is there a command that would initiate sendmail to send all the mails > now? The user has not root-privileges on our machine of course. In the privacy flags section of sendmail.cf, there is a definition Opgoaway,restrictqrun Remove restrictqrun to allow non-root users to start the queue processing. You might also like to rearrange the MXs. We are the 1st MX for our customers like this, and we have defined: # If we are the best MX for a host, try directly instead of generating # local config error. OwTrue That way a remote site will deliver straight to you, without trying the customer connection. You then send to your customer. Only works for hosts, so you need to get your customer to name their mail machine customer.com as well as hostname.customer.com in the DNS. Just put an A record in the DNS for customer.com.


Why do I keep getting Relaying Denied errors when sending mail from other hosts?

In a default FreeBSD installation, Sendmail is configured to only send mail from the host it is running on. For example, if a POP server is available, users will be able to check mail from remote locations but they will not be able to send outgoing emails from outside locations. Typically, a few moments after the attempt, an email will be sent from MAILER-DAEMON with a 5.7 Relaying Denied.

The most straightforward solution is to add the ISP's FQDN to /etc/mail/relay-domains, as seen in this example:

# echo "your.isp.example.com" > /etc/mail/relay-domains

After creating or editing this file, restart Sendmail. This works great if the server administrator does not wish to send mail locally, would like to use a MUA on a remote machine, or would like to use another ISP for remote connections. It is also useful when there is only one or two email accounts. If there are a large number of addresses, add them one per line:

your.isp.example.com other.isp.example.net users-isp.example.org www.example.org

Now any mail sent through the system by any host in this list, provided the user has an account on the system, will succeed. This allows users to send mail from the system remotely without opening the system up to relaying SPAM from the Internet.

All FreeBSD documents are available for download at http://ftp.FreeBSD.org/pub/FreeBSD/doc/

Questions that are not answered by the documentation may be sent to <freebsd-questions@FreeBSD.org>.

Send questions about this document to <freebsd-doc@FreeBSD.org>.