This section really only applies to POP3 and IMAP users; otherwise, sending mail is already set up, and you don't need to worry about it.
If you want to send mail using a tentacle.net address, you'll need to send it using the tentacle.net SMTP server. This is because spammers have started using tentacle.net as a fake "from" address, so when other servers reject those messages, all of those error messages come back to us, even though we had nothing to do with the problem. As a solution, tentacle.net has an SPF record installed, which says that any mail coming from a tentacle.net address must pass through one of its publicly listed mail servers. That means you can no longer use your own ISP's mail server for sending as a tentacle.net user. That's not a problem, though, as you can use tentacle.net as a SMTP server.
If you're using a desktop mail client, you can enable it by setting your outgoing mail server to point to tentacle.net, and by turning on SMTP authentication. This means that whenever you send an email, your email client logs in to the server in order to prove that you're an authorized user. Once that's done, you can send your mail through the system. The username and password for SMTP AUTH are the same as your normal tentacle.net username and password.
If you are familiar with SMTP AUTH, you should know that our system only supports the PLAIN and LOGIN methods, and STARTTLS is required. Some older mail clients don't work with those methods, or don't support TLS. If that's true, then you can't use the tentacle.net server for outgoing mail.
Some Internet providers block traffic on the default SMTP port (port 25), so you won't be able to use that for sending mail. Instead, tell your mail client to use port 587 for SMTP.
Outlook users should not use Secure Password Authentication (SPA); that's not the same thing, and it won't work.