Sieve basics and Dovecot extensions

Sieve (RFC 5228) is a small declarative language for mail filtering. Dovecot's Pigeonhole interpreter supports the full standard plus useful extensions.

Example: file by sender + tag urgent:

require ["fileinto", "imap4flags"];

if header :contains "from" "alerts@stripe.com" {
  fileinto "INBOX/Finance";
  setflag "\\Flagged";
  stop;
}

if header :contains "subject" "[URGENT]" {
  setflag "\\Flagged";
}

if address :is "to" "newsletter@example.com" {
  fileinto "INBOX/Newsletters";
}

Useful Dovecot Sieve extensions: