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Change mail attachment size

To change mail attachment size, we have to change 3 settings.

Change message size limit in postfix

Postfix is MTA, so we have to change its setting to transfer mail with large attachment.

For example, to allow mail with 100Mb attachment, please change both message_size_limit and mailbox_size_limit settings like below:

# postconf -e message_size_limit='104857600'
# postconf -e mailbox_size_limit='104857600'

Restart postfix to make it work:

# /etc/init.d/postfix restart

NOTES:

104857600 is 100 (MB) x 1024 (KB) x 1024 (Bit).
Mail will be encoded by mail user agent (Outlook, Thunderbird, etc) before transferred, the actual message size will be larger than 100MB, you can simplily increase above setting to 110Mb or 120Mb to make it work as expected.
If mailbox_size_limit is smaller than message_size_limit, you will get error message in Postfix log file like this: fatal: main.cf configuration error: mailbox_size_limit is smaller than message_size_limit.

If you use mail clients such as Outlook, thunderbird to send mails, it's now ok to sent large attachment with above setting.

If you have Roundcube webmail, please change two more settings:

You should change memory_limit, upload_max_filesize and post_max_size in PHP config file /etc/php.ini

on RHEL/CentOS: it's /etc/php.ini
on Debian/Ubuntu, it's /etc/php5/apache2/php.ini
on FreeBSD, it's /usr/local/etc/php.ini for Apache, or /etc/php5/fpm/php.ini for Nginx.
on OpenBSD, it's /etc/php-5.4.ini. If you're running different PHP release, the version number 5.4 will be different.

memory_limit = 200M;
upload_max_filesize = 100M;
post_max_size = 100M;

Change same settings in file .htaccess under roundcube root directory:

on RHEL/CentOS, it's /var/www/roundcubemail/.htaccess
on Debian/Ubuntu, it's /usr/share/apache2/roundcubemail/.htaccess or /opt/www/roundcubemail/.htaccess.
on FreeBSD, it's /usr/local/www/roundcubemail/.htaccess
on OpenBSD, it's /var/www/roundcubemail/.htaccess

Note: this .htaccess file may not exist on some Linux/BSD distributions, if it doesn't exist, you can skip this step.

php_value    memory_limit   200M
php_value    upload_max_filesize    100M
php_value    post_max_size  100M

Restart Apache or php-fpm service to make it work.

Find setting client_max_body_size in Nginx config file /etc/nginx/nginx.conf, change it to a proper value to match your need.

``` http { ... client_max_body_size 100m; ... }

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