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Fri, 02 Sep 2011

/Admin/email/deliverability: You Want Your E-mail Delivered: Simple Steps

You want the e-mail your mail server sends out delivered to an inbox, not to a SPAM folder. And certainly not bounced. Here are the simple things that you can do:

FQDN: Make sure your e-mail server, when communicating with other e-mail servers, identifies itself with a Fully Qualified Domain Name (FQDN). For a postfix server, an easy way to do this is add a line like the following to /etc/postfix/main.cf:
myhostname = hostname.domain.com
Reverse DNS: You cannot set this in the DNS settings for your domain names. This is something special that must be done at a higher level. If available, your website host / server provider will probably offer this setting, not your DNS provider. Set the reverse DNS for the IP address of your mail server to the most important domain name whose e-mail your mail server is responsible for.
SPF: Sender Policy Framework (SPF) is a DNS TXT record that tells receiving e-mail servers what IP addresses to accept e-mail from for a given domain. Here[1] is some online documentation that gives a pretty good idea of what the SFP TXT DNS record should look like. This DNS record:
domain.com TXT "v=spf1 mx -all"
says that a server should only accept e-mail for domain.com from a server with the same IP address as domain.com's MX record. This DNS record:
domain.com TXT "v=spf1 a -all"
says that a server should only accept e-mail for domain.com from a server with the same IP address as domain.com's A record. This
domain.com TXT "v=spf1 mx a ip4:122.248.255.249 include:_spf.google.com -all"
directs a server to accept e-mail from this domain from several sources, including Google's mail servers[3].
dig +short domain.com txt
will display domain.com's current TXT record(s).

port25.com[2] provides an excellant facility for testing your setup. Send an e-mail from your e-mail server to check-auth@verifier.port25.com or check-auth2@verifier.port25.com and they will send you an e-mail back showing your e-mail's hostname and SPF status, among other things.

[1] http://www.openspf.org/SPF_Record_Syntax
[2] http://www.port25.com/domainkeys/
[3] https://www.google.com/support/a/bin/answer.py?hl=en&answer=178723

posted at: 06:58 | path: /Admin/email/deliverability | permanent link to this entry

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Fri, 02 Sep 2011