Testing Odoo outgoing e-mail without a real mail server

Odoo 19 · Python 3 · checked on macOS

Settings > Technical > Outgoing Mail Servers has a Test Connection button. When it answers "No response received. Check server address and port number." after about 25 seconds, the credentials were never tried: the TCP connection did not complete.

1. Is it the port or the account?

Probe the port from the machine that runs Odoo, and compare with a host you know works. A timeout and an immediate refusal mean different things.

import socket
for host, port in [("smtp.example.org", 25), ("smtp.gmail.com", 25), ("smtp.gmail.com", 587)]:
    s = socket.socket(); s.settimeout(8)
    try:
        s.connect((host, port)); print(host, port, "open", s.recv(80)[:60])
    except Exception as e:
        print(host, port, type(e).__name__)
    finally:
        s.close()

Result	Meaning
`TimeoutError` on 25, but 587 connects	Your network drops outbound port 25. Many ISPs do. Not an Odoo or credentials problem.
`ConnectionRefusedError` (fast, ~0.2 s)	The host answered and nothing listens on that port. Use the port the provider documents.
Connects, banner shown, Odoo still fails	Now check encryption (none / STARTTLS / SSL) and the login.

2. Capture mail locally instead

To check what a template looks like you do not need delivery at all. Run a sink that accepts any message and writes it to disk:

python3 smtp_sink.py 1025 mail-sink

Source: smtp_sink.py. It uses only the standard library, handles the dot-stuffing of the SMTP DATA command, and ignores a client that hangs up early (a port probe, for example).

Then edit the outgoing mail server in Odoo:

SMTP Server	`127.0.0.1`
SMTP Port	`1025`
Connection Security	None
Authentication	none needed (leave user and password empty)
From Filter	empty

Each message lands as mail-sink/0001-recipient.eml. Open it in a mail client, or read the HTML part in a browser.

3. "Sent" in the UI is not "delivered"

An action that queues mail (mail.mail with a cron) returns success at once. The real result is the state and failure_reason of the mail.mail record and the Odoo log. A custom log row that says sent may only mean "queued". When a button seems to do nothing, look there first:

select id, state, left(failure_reason, 120) from mail_mail order by id desc limit 5;

One failure I hit this way came from the provider, not from Odoo: SMTPDataError (500, ... Failed to send mail No balance). A temporary mailbox service had a send quota, and a script using smtplib directly got the same error, which ruled Odoo out.

4. A real server for staging: Lark Mail

If a staging environment needs real delivery, Lark Mail can be used as an SMTP server for an address on a domain you control. From Lark's documentation:

Outgoing server: smtp.larksuite.com, SSL, port 465.
A separate password for third-party clients is generated in the Lark desktop app (Settings > Email > Third-party email client login). The mobile app and the web version cannot generate it.
An administrator must switch the third-party client permission on first (Admin Console > Product Settings > Mail > Email Management Tools > User Function Permissions).
The account needs a business e-mail address assigned on a verified domain, or Lark shows No email address.

Set the Odoo From Filter and the mail.default.from system parameter to that same address, so the sender matches the login.