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Change mail attachment size

Change mail attachment size

Mail attachment size is configured in multiple places with default iRedMail settings:

Postfix is the MTA, it checks the size of each received and sent message.
Dovecot is the LDA (local delivery agent), it checks mailbox size (a.k.a. mailbox quota)
Nginx / Apache is web server, if you upload mail attachment via webmail, web server checks the size of uploaded mail attachment.
Roundcube webmail, SOGo have their own message size limit settings, but they're not enabled by iRedMail by default, so they use web server upload size instead.
Desktop mail client application like Outlook may have its own message size limit.

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

Note

They don't have to be same. but mailbox_size_limit (size of the mailbox) MUST be equal to or LARGER than message_size_limit (size of single email message).
Postfix is configured to pipe received email to Dovecot for local mail delivery, so the mailbox_size_limit setting is not used, but we still need this setting to surpress Postfix warning while starting Postfix service.

Restart postfix to make it work:

# /etc/init.d/postfix restart

NOTES:

104857600 is 100 (MB) x 1024 (KB) x 1024 (Byte).
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.

Change upload file size in Roundcube webmail

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

Change PHP setting to allow to upload large attachment

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 Ubuntu 16.04 and later releases, it's /etc/php/7.0/apache2/php.ini for Apache, or /etc/php/7.0/fpm/php.ini for Nginx + php-fpm.
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 Roundcube webmail settings to allow large attachment

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.

Change upload file size in Nginx

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;
    ...
}

Change file size limits in SOGo

SOGo config file is /etc/sogo/sogo.conf (Linux/OpenBSD) or /usr/local/etc/sogo/sogo.conf (FreeBSD), 2 settings are relevant to message size:

SOGo-3.x introduces parameter WOMaxUploadSize to limit upload file size.
SOGo-3.2.5 introduces parameter SOGoMaximumMessageSizeLimit to limit single message size.

    // set the maximum allowed size for content being sent to SOGo using a PUT or
    // a POST call. This can also limit the file attachment size being uploaded
    // to SOGo when composing a mail.
    //
    //  - The value is in kilobyte.
    //  - By default, the value is 0, or disabled so no limit will be set.
    WOMaxUploadSize = 102400;

    // Parameter used to set the maximum allowed email message size when
    // composing a mail.
    // The value is in kilobytes. By default, the value is 0, or disabled so
    // no limit will be set.
    SOGoMaximumMessageSizeLimit = 102400;

Restarting SOGo service is required if you changed any setting in SOGo config file.

Change attachment size limit in Microsoft Outlook

Outlook has its own attachment size limit, and will raise error like The attachment size exceeds the allowable limit.

To modify the default attachment limit size in Outlook on Windows system, follow these steps:

Exit Outlook.
Start Registry Editor.
Locate and then select one of the following registry subkeys:
- Manually create the path in the registry if it does not currently exist.
- `14.01 means Outlook version number, it may be different on your system.

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\Preferences

Add the following registry data under this subkey:
- Value type: DWORD
- Value name: MaximumAttachmentSize
- Value data: An integer that specifies the total maximum allowable attachment size. For example, specify 30720 (Decimal) to configure a 30-MB limit.
Notes:
- Specify a value of zero (0) if you want to configure no limit for attachments.
- Specify a value that is less than 20 MB if you want to configure a limit that is less than the default 20 MB.
Exit Registry Editor
Start Outlook.

Reference: https://support.microsoft.com/en-us/kb/2222370