Roundcube - Connection Error - Sending a particular email

A strange problem. All works well except

Few emails cant be forwarded or replied with original content

Genuine emails (ex: from Bank)

Where to check the logs to find the issue?

On clicking the send message, I get this error flashed for a second

Connection Error. (Failed to reach the server)

Roundcube logs:

/usr/local/cwpsrv/var/services/roundcube/logs/errors.log

Mail logs:

/var/log/maillog
/var/log/dovecot.log

If there is nothng inside Roundcube logs, check the section "LOGGING/DEBUGGING" of the file:
/usr/local/cwpsrv/var/services/roundcube/config/defaults.inc.php
and change the settings according to your requirements.

Did you check ModSecurity? Look at disabling rule 212880 or others that may be interfering with Roundcube.

Cyberspace, glad to have you back! Always hoping you are staying safe over there!

Checking.

Looks like unable to forward any email

I can compose and send a new email.

But I cant reply / forward any email

Not getting any clue from logs.

I tried disabling mod security / adding the exception. No use.

Please advise the following:

What distro are you running CWP on?

Public or NAT?

Can you send out a test email form the CLI?

--

Welcome back @cyberspace

Looks like disabling mod security for the domain , mails are going

Adding id 212880 not helping. Maybe other IDs need to be checked.

Check the ModSecurity log file for that domain, and it should show which rule was being triggered.