Hi,

In Odoo Online 18.3, even if the outgoing mail server connection test succeeds, emails may not be sent if they are not being queued. In your case, no messages appear under Technical → Emails → Outgoing, indicating a problem with email generation rather than delivery. This often happens on Odoo Online because the system requires verified sending domains for security and compliance.

The likely causes include an unverified domain, a mismatch between the sender email in templates and the verified domain, or improperly configured email templates. Unlike on-premise setups, Odoo Online may restrict SMTP sending if the domain is not verified or the From address is unauthorized.

To resolve this, you should verify your domain in Odoo Online by adding SPF and DKIM records in cPanel, ensure all email templates use a sender that matches the verified domain, and then resend test emails. Once the domain is verified and templates correctly configured, emails should be queued and sent automatically via the mail scheduler.

For more reference:

* https://www.cybrosys.com/blog/how-to-configure-outgoing-and-incoming-mail-servers-in-odoo-18

*https://www.odoo.com/documentation/18.0/applications/general/email_communication/email_servers_outbound.html

Hope  it helps

Hello.

Odoo Online or odoo. sh Users

Since Odoo sets up its own mail servers for the database, outgoing and incoming emails already work out-of-the-box. So for Odoo Online and odoo.SH customers, nothing needs to be configured!

Unless an external mail server is required to send large batches of mass emails, simply use the standard online Odoo database normally since it has already been pre-configured to send email. 

Check below for official documentation:

https://www.odoo.com/documentation/16.0/applications/general/email_communication/email_servers.html#odoo-online-or-odoo-sh-users