I have a problem with configuration of SMTP using SwiftMailer, which I managed to solve it temporarily. I changed the password from my mailer and I changed the settings at the SMTP's config file too with the updated one for registration usage at my website.
While the registration was working perfectly at local using WAMP, when a new user was trying to register at the website the confirmation e-mail was sent to the user's mail correctly and everything was fine, but this didn't work at the online version of the site, while I changed the same parameters in server's file too.
I didn't make any changes at the code so the coding is working well. When I looked at the log files of the server, the error seemed to be "Failed to authenticate on SMTP using 2 possible authenticators", so I changed the password back to the previous one and registration is working perfectly at the online version too.
I think that there is a possibility that the SMTP is taking the previous settings from some cache files? Is it possible to happen? And how can I deal with this?
You probably have to clear symfony cache, so new setting will take effect (on production env). This is for symfony 3.
php bin/console cache:clear --env=prod
You could manually send email via swift mailer (how to spool emails) and you will have to provide all the parameters when asked:
php bin/console swiftmailer:spool:send --env=prod