Unable to log into webmail under specific user: Response body too large

Symptoms

• In an attempt to log into Roundcube webmail under specific user, it fails with the error:

  external server error

• At the same time the following can be found in /var/log/httpd/error_log or /var/log/modsec_audit.log log file:

  [:error][client 203.0.113.2] ModSecurity: Output filter: Response body too large (over limit of 524288, total not specified). [hostname "webmail.example.com"] [uri "/roundcube/index.php"] [unique_id "XvMRFl1Q0bEa9Qiy1@TmewAAAEU"], referer: https://webmail.example.com/roundcube/?_task=mail&_mbox=INBOX

Cause

Webmail exceeded the default SecResponseBodyLimit parameter for ModSecurity (512 Kb).

Resolution

1. Log in to Plesk.

2. Go to Tools & settings > Web Application Firewall (ModSecurity) > Settings.

3. Add the following line into the Custom directives section:

   SecResponseBodyLimit 546870912

4. Scroll down and press the OK button to apply the changes.