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Sat, 04 Oct 2008

/Admin/email/postfix: Simple E-mail Server Relay

The obvious first thing to try is an unauthenticated relay through your ISP's e-mail server: since I am a paying ADSL customer within their network, hopefully authentication will not be necessary. My ISP is China Netcom (中国网通 - “Wang Tong”). From China Netcom's e-mail web page I deduce that one of their servers is smtp.bbn.cn. If I add

relayhost = smtp.bbn.cn

to /etc/postfix/main.cf, my e-mails bounce with the error “530 Authentication required”, ie. for this SMTP server I need to set up a China Netcom/网通 e-mail account and use authenticated relaying.

I then set up a bbn.cn account on http://mail.bbn.com.cn/. Note that if you are not using a China Netcom/网通 internet connection, you will get the following error message when you attempt to register: “提示：请您使用北京网通宽带接入才能购买此产品”. Also note that if you cannot read Chinese then the translation function of www.xuezhongwen.net/chindict/chindict.php is your friend.

I then tested my new bbn.cn account's SMTP with my regular e-mail client, and it seemed to work fine. I then configured my postfix server to relay ALL e-mails through my bbn.cn account:

First edit /etc/postfix/sasl_passwd to contain:

smtp.bbn.cn username:password

Restrict access to this password file:

chown root:root /etc/postfix/sasl_passwd && chmod 600 /etc/postfix/sasl_passwd

Create a database version of the file (sasl_passwd.db) for postfix:

postmap hash:/etc/postfix/sasl_passwd

Now edit /etc/postfix/main.cf to add the following lines:

relayhost = smtp.bbn.cn
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_type = cyrus
smtp_sasl_security_options = noanonymous

and restart postfix:

/etc/init.d/postfix restart

You can then verify that your server’s outgoing e-mails are passing through smtp.bbn.cn by examining the header of a sent e-mail. Also, in /var/log/mail.log you should also see something like:

postfix/smtp[7052]: 34CEA238D8: to=user@email.com, relay=smtp.bbn.cn[202.106.46.89]:25, delay=1388, delays=1382/0.11/5.6/0.14, dsn=2.0.0, status=sent (250 ok: Message 135909587 accepted)

Sadly, there seems to be a problem with smtp.bbn.cn, as some of my e-mail disappeared without a trace or a bounce. Bad server. Stay away from smtp.bbn.cn.

But the process is very easy to replicate. Next I registered for a sohu.com e-mail account at mail.sohu.com and substituted:

relayhost = smtp.sohu.com

in /etc/postfix/main.cf. (And don't forget the correct userid/password for your sohu.com account in /etc/postfix/sasl_passwd...)

smtp.sohu.com seems to be reliable in the sense that they do not lose my e-mail, but if there is a lot of outgoing mail in a short period, they start refusing service and finally bounce everything for a period of time until things quiet down. In other words, a simple relay through sohu will probably work for personal e-mail, but if you have other people using your server this will probably not be the final solution.

I am running now on a somewhat more complicated configuration: a multiple relay.

posted at: 08:21 | path: /Admin/email/postfix | permanent link to this entry

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Sat, 04 Oct 2008