I may have found a lead.

I think there is something on the sending host that is not matching ssl requirements for the mail server.
The component is not able to deal with the problem which might be why the back-end gets a geteway error.

This is just early findings, not sure what the problem is yet. Maybe if I solve the host problem, then it might provide a little hint on why the back-end does this as well.

Trying 6.6.
First, it won't let me leave the username/password blank so I have to enter something.
Now the mail server is getting the connection instead of the email being sent directly.
However, I'm seeing something I never seen from any other host sending mail to the mail servers.

Oct 12 10:57:49 mx postfix/smtps/smtpd[28034]: warning: TLS library problem: error:14094418:SSL routines:ssl3readbytes:tlsv1 alert unknown ca:ssl/record/reclayers3.c:1563:SSL alert number 48:

This is happening no matter if I use port 25 or 465.

Hosts are always up to date, have proper SSL certs for web services so I don't what the mail server is complaining about. I have to dig more into this.

As for why I'm not using a dev server, because it's internal and sometimes I have help from remote so made a site public that can be used for testing as well. It's not being advertised or promoted yet.

Try 6.6 version of the component https://github.com/opensource-socialnetwork/SMTP/releases/tag/6.6

In case it fails, try to debug the SMTP and see what is the issue using, debug the SMTP component (smtp debug method) .

Also I see that you are running paid ossn on local instances only for development so why don't you just use fake mail SMTP settings if you just wanted to test our the mails?

Hi,

The component requires an authentication but LAN hosts that have sendmail are always allowed to relay to a LAN mail server on our subnets.
Also, we don't use port 25 so when I try using 465 for example, and save, then I get a gateway timeout on the back-end while the front-end continues working as usual.

So far, cannot really test it correctly and would prefer just using php's mail function over phpmailer or a component.
BTW, this happened on firefox, chrome and brave. After getting the 501, I had to actually restart the apache/php services.

Totally weird so not really sure what happened in this case.

You wrote:
"... we have a mail server on the LAN and all hosts use sendmail to relay to that host..."
"... that smtp component is useless for me as far as I can see ..."
That is

Ossn server with SMTP component configured to connect your Mail server

doesn't work?

Well, configuring email is not a new thing for me and the directives are set correctly in php.ini to use sendmail which then relays to a mail server. As mentioned, something is bypassing sendmail. The bounces clearly show the emails are coming from this host and going out directly instead of being sent to a mail server.

I'll have to take a closer look tomorrow.

This is also phpmailer doesn't control its your php ini settings anyway you can edit the mail class

Edit OssnMail class and use your own changes inside

Ossn seems to be using phpmailer. I need it to NOT use that and to use php's sendmail directive.
How can this be done?

I have moved your threads here instead of making other thread owner getting unwanted emails.

Again I would like to mention OSSN is not controlling this. Mail is sent by default php mail() method. You should better approach phpmailer community for this and discuss it with them.