I changed the SMTP Server in Outgoing E-mail Settings (Central Admin). But now is not sending mail.
Do you have any idea what that might be? Do I need to make more changes?
Make sure that your SharePoint server are registered for smtp rely to send the emails.
Also check if there is any firewall blocking issue between SharePoint and new smtp servers.
Try to send the email on SharePoint servers using command-line
Also enabled verbose logging and check the uls log to get the clue why it is not sending email.
Make Sure whether all web application cannot send alert email .
Two points need check :
CA --System Settings --Configure outgoing e-mail settings . check the SMTP server was configured correctly .
CA --Application Management -- Manage web application --select your web application and click General Settings --outgoing e-mail , verify the settings is correct .