External Email Warning Message

su - zimbra

vi /opt/zimbra/conf/disclaimer-external.conf

Fill it with the following lines:

use strict;

$altermime='/opt/zimbra/common/bin/altermime';

@altermime_args_disclaimer = qw(--verbose --pretext=/opt/zimbra/data/altermime/_OPTION_.txt --pretext-html=/opt/zimbra/data/altermime/_OPTION_.html --force-for-bad-html);

$defang_maps_by_ccat{+CC_CATCHALL} = ['disclaimer'];

$allow_disclaimers = 1;

@local_domains_maps = (["."]);

@disclaimer_options_bysender_maps = ({

        '.' => 'external_domains',

},);

1;

Create external_domains.html and external_domains.txt files

vi /opt/zimbra/data/altermime/external_domains.txt

CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.

vi /opt/zimbra/data/altermime/external_domains.html

<div style="background-color: #ffeb9c; width: 100%; padding: 2pt; font-size: 10pt; line-height: 12pt; font-family: 'Calibri'; color: black; text-align: left; border: 1pt solid #9C6500;"><span style="color: #9c6500;">CAUTION:</span> This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div>

vi /opt/zimbra/conf/amavisd.conf.in

include_config_files('/opt/zimbra/conf/disclaimer-external.conf');

zmamavisdctl restart

Ref: https://imanudin.net/2020/10/17/zimbra-tips-how-to-add-external-email-warning-message/