Log contains link to PHPmailer

My campaign and my test emails are failing. I visit System>Log of Events and there’s an entry for every email, and each one contains this message:
Error sending email to xxx@yyyzzz.com SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting

No real information regarding the error, and the link points to PHPmailer. What am I supposed to do with this?