Nowadays, e-mail is still the most preferred way of electronic communication. Making sure that e-mail emission from Redmine works flawlessly and that e-mails don't end up as spam or that your mail server is not hacked or abused is very important. This recipe tries to address some of the most common e-mail configuration issues. Many problems with Redmine configuration are related to e-mail sending and properly sending e-mails so that they don't end up as spam.
Make sure that you have a user account ready to send e-mail on the SMTP server. Also, make sure that your server is properly configured and secured and your reverse DNS records are entered.
Tip
You can use a free service, such as http://mxtoolbox.com/, to check your e-mail server's configuration.