Skip to main content

Postfix: smtp_address_preference

For mailserver/system  administrator :

If your mailserver has problem to connect to ipv6 address (especially if your mailserver doesn't support it) and throw errors something like this:

Dec 10 00:05:57 localhost postfix/smtp[16925]: connect to mta7.am0.yahoodns.net[2404:160:0:f:0:2:42c4:7621]:25: Network is unreachable
Dec 10 00:05:57 localhost postfix/smtp[16925]: connect to mta6.am0.yahoodns.net[2404:160:0:f:0:1:6288:d9ca]:25: Network is unreachable
Dec 10 00:05:57 localhost postfix/smtp[16925]: connect to mta7.am0.yahoodns.net[2404:160:0:f:0:2:42c4:7624]:25: Network is unreachable
Dec 10 00:05:57 localhost postfix/smtp[16925]: connect to mta6.am0.yahoodns.net[2404:160:0:f:0:1:43c3:a8e6]:25: Network is unreachable
Dec 10 00:05:57 localhost postfix/smtp[16925]: connect to mta6.am0.yahoodns.net[2404:160:0:f:0:1:42c4:7622]:25: Network is unreachable

then you may want to check the default smtp_address_preference parameter in main.cf. Most probably it is defaulted to ipv6 which is true on my postfix installation (Mageia). Change it to ipv4 to instruct postfix to look up MTA with ipv4 address only (which is I think supported by all major players like Yahoo!, Gmail and Hotmail for compatibility reason or they will lose lots of their customers) . So:

smtp_address_preference = ipv4

will save you before you consider to upgrade your infrastructure to ipv6. :-)

Have fun!

Comments

Popular posts from this blog

mplayer-gui error : Error in skin config file

After installing mplayer-gui package, I can't start it.

$ gmplayer MPlayer 1.1-4.8 (C) 2000-2012 MPlayer Team mplayer: could not connect to socket mplayer: No such file or directory Failed to open LIRC support. You will not be able to use your remote control. Error in skin config file on line 6: PNG read error in /usr/share/mplayer/skins/default/main Config file processing error with skin 'default'
After googling a bit, I found out that it was due to the png files in dir /usr/share/mplayer/skins/default. This is the default skin directory. To fix this error, I have to install ImageMagick package because I want to use the convert program to convert all of the png files to format png24. Thus, cd /usr/share/mplayer/skins/default; for FILE in *.png ; do sudo convert $FILE -define png:format=png24 $FILE ; done
Rerun gmplayer and all should be fine.
Have fun!
UPDATE (02-10-2017)

It doesn't work on Ubuntu 16.04 (xenial) but there's a workaround here.

You can update your syst…

Transparent proxy with squid 2.6

I have upgraded my squid from 2.5 STABLE13 to 2.6 STABLE18. Transparent proxy is setup differently in this version. You need this directives in squid.conf (usually in /etc or /usr/local/etc or /usr/local/squid/etc, check with your distro).

acl our_networks src 192.168.2.0/24 127.0.0.1
http_access allow our_networks
http_port 192.168.2.1:3128 transparent
always_direct allow all

where 192.168.2.1 is your proxy server IP address.


If you have flushed your iptables, create new rule:

iptables -t nat -A PREROUTING -i eth0 -p tcp –dport 80 -j REDIRECT –to-port 3128

where 3128 is the port where squid is running.
References:
http://www.deckle.co.za/squid-users-guide/Transparent_Caching/Proxy

postfix - mailbox size limit and message size limit

postfix is my MTA of choice. I use it for my mailserver because its simplicity , security and sendmail-compatible (the widely used smtp in the world but not as secure). It is also extensible by plugging other servers for various purposes (antispam, antivirus,database etc).

I had one problem with file attachment larger than 10MB. Users couldn't send it although I have setup squirrelmail (SM) to be able to attach files summed up more than 20MB and I had modified php settings as per here. The problem was not in SM setting. It was postfix. By default, attachment size that can be sent by postfix is 10MB ~ 10240000 byte. How did I know it? I looked in log file (for my system it is in /var/log/mail/errors. For other system, the file to look is /var/log/maillog). The line looked like this:

Feb 26 16:30:53 webmail postfix/sendmail[30775]: fatal: me@mymailserver.org(74): Message file too big


Solution
Open /etc/postfix/main.cf with a text editor of choice and find message_size_limit directive an…