Too late to edit.

The reason for asking about removing auth is that user accounts have to change their passwords every 60 days or so which means if the credentials are overlooked on the ossn server, it will lose emails.

Finally got it to work but I'm not sure why since I've done this before.
I think it's because I used the mx FQDN instead of the IP while testing.

Anyhow,
Mail server: FQDN
Port: 25
Username: aaa
Password: bbb
Saved then saw "SMTP Connection successfully established".

Tested and it sent to gmail via the mail server.

I should not have to use credentials however as the mail server allows all hosts on the lan to send.
Do you think you could update the smtp component to allow this?

Too early to tell but some good news at least.

When I test from the command line it's always good.

openssl s_client -connect mx.domain.com:25 -starttls smtp

No errors what so ever, ssl/tls all good. Only when sending from ossn do I see all these problems and immediate disconnections from the mail server.

Also, if I use port 443 in the smtp config, it kills the site. I have to restart the web service and change the url to /administrator. If the url is /administrator/smtp, then the site gets a gateway timeout.

By the way, no matter how I set it up, the smtp component never shows 'SMTP Connection successfully established'.

I do have the ossn host connecting to the mail server to use as a relay now.
Without the smtp component, it only gets sent directly to remote servers which is bad.

When I test using the smtp component, this is what I get on the mail server log. 10.0.0.182 is the ossn server.

Port 25, 465 and 487 have the same result. With or without authentication credentials, same thing.

Oct 20 18:20:16 mx postfix/postscreen[11653]: CONNECT from [10.0.0.182]:42070 to [10.0.0.100]:25
Oct 20 18:20:16 mx postfix/postscreen[11653]: ALLOWLISTED [10.0.0.182]:42070
Oct 20 18:20:16 mx postfix/smtpd[11654]: connect from unknown[10.0.0.182]
Oct 20 18:20:17 mx postfix/smtpd[11654]: Anonymous TLS connection established from unknown[10.0.0.182]: TLSv1.3 with cipher TLSAES256GCMSHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256
Oct 20 18:20:17 mx postfix/smtpd[11654]: lost connection after STARTTLS from unknown[10.0.0.182]
Oct 20 18:20:17 mx postfix/smtpd[11654]: disconnect from unknown[10.0.0.182] ehlo=1 starttls=1 commands=2
^C

It gets disconnected right away. If I disable strict tls checking on the mail server, then it works, sometimes but I don't want to do that on the mail server.

At least the ossn server is reaching the mail server so I have no idea why no matter how I test, it never works, only gets disconnected with " lost connection after STARTTLS from unknown[10.0.0.182]".

Yes, 587 works. I have scripts that send emails from different hosts every day and those work fine.
The mail server accepts 25, 465 from remotes and 587, imap/s and pop/s from users.

I had it working for one test but have yet to figure out why that worked and it's not since.
There are no errors/logs on the ossn server unless I enable some debugging but what I need is to have phpmailer use the php mail function which is what it doesn't seem to be doing.

I don't know, this has lead me down a huge rabbit hole of other issues I have to solve before I can get back to this now.

Again, and to focus on the most hassle free variant:
You can confirm that sending a mail with Thunderbird configured to connect to

Your_mail_server, Port 587

works without issues, but

using Invite Friends (same email address) on your Ossn server
- running Ossn 7.1
- with SMTP component 6.6 installed
configured to connect to

 Your_mail_server, Port 587, Does this relates to OAUTH2: No

does NOT work.

Okay, then what message do you get from the SMTP component?
- SMTP Connection Failed
or
- SMTP Connection successfully established

The mail server works fine as other hosts are able to relay and mailers are working correctly as well.
From the command line, I cannot use port 25 but I can use 465 (with errors) and 587 CLI sent emails are accepted.

From the SMTP component, nothing works, on any of the above ports. However, port 465 always causes the app to hang. Only a web service restart gets it back.

So, my update is, still working on it, still do not have a solution.

Any status on this please?

I'd try the following cross-check:
Configure a mail-client like Thunderbird using the same credentials as used by the SMTP component
and see the postfix log after sending a mail via Thunderbird