Emails are not delivered

check if email is not landing in spam, in headers of email message you can check what is reason for it to land in spam
Check if mailbox you set in app, delivers emails send through email client, you can use for that Thunderbird, Roundcube or similar software.
Check if mailbox address, from which you send emails, match “Email address used in from field of email message” in classified app settings (URL: /admin/red5/settings/system-settings).

for most cases to email address be deliverable you must set DKIM and DMARC
check if spf records are set correctly
- ip address from where you send email must be included in your email’s address spf record, for example spf record in domain’s DNS records allows ip address of 88.99.224.187 to send emails from mailboxes in this domain

"v=spf1 a mx ipv4:88.99.224.187 -all"

full documentation of sending emails is available here:

you can change mailer configuration manually by modyfying value of MAILER_URL in configration file:

zz_engine/.env.local.php

to send email using local sendmail change MAILER_URL to:

'MAILER_URL' => 'sendmail://default',