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Change mail attachment size


Check out the lightweight on-premises email archiving software developed by iRedMail team: Spider Email Archiver.

Mail attachment size is configured in multiple places with default iRedMail 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


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

Change message size limit in iRedAPD

With plugin throttle enabled in iRedAPD config file (/opt/iredapd/, iRedAPD will query throttle settings from SQL database (SQL table iredapd.throttle), if there's a global, per-domain or per-user message size limit set for sender or recipient, it will performs the check.

Both Postfix and iRedAPD check the size of single message, if the message size reaches the limit of either Postfix setting or iRedAPD throttle setting, the email will be rejected.

You can set the throttle with iRedAdmin-Pro, or with SQL command tool, for more details, please check plugin source file, it's documented with examples and explanation: Throttle plugin.

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

Change PHP settings to upload large file

Please also update PHP config file php.ini to allow uploading large file:

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


Roundcube webmail

Roundcube 1.3.0 and later releases use its own setting max_message_size to limit message size, please add or update this parameter in its config file:

$config['max_message_size'] = '100M';

Note: Roundcube preserves some percentage of the max message size (search 1.33 on this page, so if you set the max to 100M, it tells you only 75MB is allowed (100 / 1.33). This is better because email messsage will be encoded before sending to MTA and the encoded attachment is larger than the original file.

Change upload file size in Nginx

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


Old iRedMail releases set this parameter in /etc/nginx/nginx.conf.

client_max_body_size 100m;

Reloading or restarting Nginx service is required.

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:

    // 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: