Email services routed through the SMTP module can encounter a timeout error if the SMTP service is unavailable or using TLS version 1.0.
phpmailerException: StartTLS not supported by server or could not initiate session. in PHPMailer->SmtpConnect()
You can test the timeout behavior by SSH'ing into your server to run the following command, replacing the SITENAME with your application’s site name and ENV with the desired environment:
SITENAME@srv-1234:/var/www/html/SITENAME.ENV/docroot$ openssl s_client -connect www.example.com:25 -starttls smtp connect: Connection timed out connect:errno=110
It's also a good idea to double check the module variables:
SITENAME@srv-1234:/var/www/html/SITENAME.ENV/docroot/sites/default$ drush vget smtp --uri=https://example.com | egrep "port|protocol|from|host" smtp_client_hostname: '' smtp_from: email@example.com smtp_fromname: 'NAME OF SITE' smtp_host: smtp-relay.example.com smtp_hostbackup: '' smtp_port: '25' smtp_protocol: tls
Contact your SMTP service to check for any service-related issues, as well as confirm the SMTP server being used has TLS version 1.2 and above. Please note support for TLS version 1.0 is deprecated on the Acquia platform.