Dovecot vs Respond.io

Dovecot is the IMAP and POP3 server behind a large share of the world's mailboxes. The 2.4 branch opened in January 2025 with a deliberately incompatible release — configuration files must be rewritten, the plugin section is gone, and several long-standing features were removed outright — and every release since has been consolidation on top of it. The pattern is consistent: each point release leads with critical CVE fixes, then lists incremental changes. The latest, 2.4.5, carries twelve CVEs alongside post-quantum ML-KEM support, full-text phrase searching and a throttling response code.

Two things are being worked at once. Security is the visible half, and the volume is striking — resource-exhaustion and parser issues in IMAP THREAD, LIST and ID, a CRIME-style compression side channel, an authentication bypass through XCLIENT forwarding. The quieter half is that fixes are increasingly gated behind version declarations: the THREAD fix needs a new index format enabled only by raising dovecot_storage_version. That mechanism, introduced with 2.4.0, is now doing real work, letting operators take format changes on their own schedule.

Experimental flags for mail UTF-8 and IMAP4rev2 have carried unchanged through every 2.4 release so far; the next branch-defining move is one of those graduating to default rather than another security round.