Hi,
also try using SMTP Server Port 587 instead of 465. If both ports don't work, maybe DIR-825 does not support SSL/TLS/STARTTLS! In this case try SMTP Server Port 25 (where password is transmitted in plain text!), but maybe this is no longer supported by Google. In this case take a mail provider who still supports SMTP via port 25 and use this mail account only for the single purpose to send the router log ...
PT