Display warning when sending SMTP email fails at registration

[Sama34]

When sending SMTP email fails during user registration the current system displays a positive notification on the screen , rather than a message indicating that something went wrong, leading to a situation where a user is expecting an email that will never be delivered.

Related: #4680

[RevertIT]

That is how it should be.

An end user should never know whether there is or isn't an issue with the internal infrastructure. Beware that $this->connection is a resource that is generated via sockets, which usually fails when there is a problem with the end server connection.

Showing when the server is malfunctioning (whatever the message is) will just lead to more potential DDoS targeting on big boards which host their own SMTP server.

[Sama34]

Probably, but something has to be done in order to improve the user experience. Perhaps log the error and display such errors to the administrators in the ACP ? Put the user automatically on admin approval ?

Regardless of the approach, users shouldn't be expecting a mail when we (the script) know such mail was never sent in the first place.

[RevertIT]

I think when there is an outage with socket connections, there are logs into the mail errors ACP section.

users shouldn't be expecting

Correct thinking, but very wrong execution in a real-life scenario. As someone who coordinated large traffic of thousands of concurrent users (unrelated to MyBB or the forum platform in general), I can tell you that showing any outage to end users ends badly (It's much safer to let users assume and be irritated whether the email was rejected by their mail provider, went into spam, not configured properly, etc, than letting them know it was exactly your infrastructure being the problem). The same goes with showing the combination of username/email was correct or not when "forgetting password" and many other similar things which on a small scale are often overlooked.