Most of the students in Baden-W√ºrttemberg are sooner or later in the situation that they're trying to send an EMail while being in university. As Belwue has blocked outgoing SMTP requests on port 25 to keep spam down to a minimum.
What most people don't know: Many EMail Providers (e.g. gmail) allow the use of Port 587 (the "SMTP Submission port";)!
Port 587 is for users to send out emails on.
Port 25 is for servers to relay messages to one another.
That way ISPs can block outgoing SMTP relays (–> mailservers) on their networks but still allow users to send email to any mail server through port 587.