I think the terminology that the “WP Mail SMTP” plugin is using on their plugin page makes this topic a bit confusing.
Plain SMTP is just an internet protocol and is the default way that WordPress (and most machines really) uses to send email. If the WordPress site is using “plain smtp” to deliver email, then Local will capture all of those emails and you don’t have to worry about anything.
But reading through the description of the WP Mail SMTP plugin definitely muddies these waters:
WP Mail SMTP plugin easily resolves email delivery problems by improving and changing how your WordPress site sends email. We reconfigure the
wp_mail() function to either use proper SMTP host credentials or leverage a built-in SMTP mail provider.
When using one of our built-in SMTP mail provider integrations (recommended), emails are sent using the provider’s direct API. This means even if your web host is blocking SMTP ports, your emails still send successfully.
Basically, the problem is the “direct API” part. It looks like this plugin is sort of a wrapper to help you configure access to third party email delivery systems (SMTP.com, Mailgun, Sendgrid, etc) via that system’s API and not the traditional smtp protocol.
If this plugin doesn’t do anything to disable its functionality depending on the WordPress environment, then yeah, I could see this plugin sending emails even from within the Local site.
Your idea to import the site, disconnect from the internet and then disable to plugin is a decent one and probably would get you what you need.
But if I were you, I’d reach out to their support and see if there are any settings or recommended workflows for using their plugin and working on a site that isn’t in production. You can’t be the only person that wants to use their plugin but also wants to do development on a site in a non-production environments.
If you do get an answer, please reply here so the community can learn more!