NoIdeaWhatThatIs other forum scripts are working simply right out of the box by providing an admin email
This usually only works if the server you run on handles the email for you, in this case you can choose the mail option in Flarum. This option will use the php native function mail() which, in its official documentation states
It is worth noting that the mail() function is not suitable for larger volumes of email in a loop. This function opens and closes an SMTP socket for each email, which is not very efficient.
Understand that that "shared mail server" is actually the one you should be communicating with. If they set up your hosting plan correctly the mail function will interact with that shared mail server on its own, given you abide to the requirements of that shared mail server (eg sending on behalf of the right email address - from).
NoIdeaWhatThatIs why a forum requires the complex route with a dedicated mail server
Flarum does not require a dedicated mail server. Most hosting plans, hosting control panels and pretty much anyone with an email address (including people using gmail, outlook etc) have the ability to send email using smtp for/on behalf of their inbox/mail address, as such this is another option natively supported by Flarum. No dedicated service is required for this.
In fact using SMTP as the mail driver is the most reliable and most flexible option that Flarum provides. Because it allows you to use any email service available, including those your hosting provider set up.
PS the error mentions the SMTP driver, so perhaps you should use the mail option from the mail selection list.
