perhaps having a “disable” switch for the entire SMTP/API transport could still be a good idea, otherwise you still need to disable the plugin completely to revert back to the default mailer…
it could be helpful in testing so you can still access the plugin, run the connection test and diagnostics and debug settings etc. on a live site, while knowing (especially if you’re having problems) that your default mail is still going out as it normally would (php_mailer without SMTP) in the meanwhile.
well, that is something I was doing the other night while testing a different plugin before I found yours (WP Mail SMTP) that has such a switch… it was *kinda* useful, in the sense of being able to send test emails with the SMTP setting *before* those settings are actually applied live.
so it *could* avoid loss of emails while setting up the plugin… and maybe a similar case would be changing the SMTP settings to a different server and testing those. I guess a similar idea is being able to disable a site cache without deactivating the cache plugin entirely. my 2c.
(total props on a great plugin by the way!)