refs tpo/tpa/tails/sysadmin#18165

tails/how-tos/spam.md

+# SPAM training guide
+
+Schleuder messages are copied to the `vmail` system user mailbox and
+automatically deleted after 3 days, so we have a chance to do manual training
+of SPAM.
+
+This happens in both mail servers:
+
+- `mail.lizard`: hosts old `@boum.org` Schleuder lists and redirects mail sent
+  to them to the new `@tails.net` lists.
+- `mta.chameleon`: hosts new `@tails.net` Schleuder lists.
+
+To manually train our antispam, SSH into one of the servers above and then:
+
+```
+sudo -u vmail mutt
+```
+
+Shortcuts:
+
+- `s` for SPAM
+- `h` for HAM (no-SPAM)
+- `d` to delete
+
+**Important:** If you're in `mta.tails.net`, do not train mail from
+`@boum.org`, but instead just delete them because we don't want to teach the
+filter to think that encrypted mail is spam.