Several SFP mail and DNS tools
MailCatcher runs a super simple SMTP server which catches any message sent to it to display in a web interface. Run mailcatcher, set your favourite app to deliver to smtp://127.0.0.1:1025 instead of your default SMTP server, then check out http://127.0.0.
Why SPF is not the best way to fight spam
RFC2821 and RFC2822 state clearly that only 7bit ASCII characters are allowed in Internet mail addresses. The following list shows all the ASCII characters and explains whether they can or should be allowed in the local part of a mail address.
Online Testseite um zu checken ob ein Mailserver als Relay agiert
SMTP Testutility - Webinterface