https://gitlab.synchro.net/main/sbbs/-/commit/32ea273f6f53272ca216a195
Added Files:
src/sbbs3/mail_dkim.c mail_dkim.h
Modified Files:
docs/v322_new.md src/sbbs3/GNUmakefile mailsrvr.cpp mailsrvr.h mailsrvr.vcxproj mime.c mime.h objects.mk sbbs_ini.c src/sbbs3/scfg/scfgindex.h scfgsrvr.c
Log Message:
mailsrvr: DKIM signing of outbound mail (issue #215)

Sign outbound messages with a relaxed/relaxed rsa-sha256 DKIM-Signature
header so receivers can authenticate them. Enabled via the [Mail]
DKIMSign / DKIMDomain / DKIMSelector keys (and the SCFG SendMail Support
menu); the RSA private key is loaded from ctrl/dkim_<selector>.pem and
the matching public key is published in DNS by the sysop.

New mail_dkim.{c,h}: streaming relaxed body hash, relaxed header canonicalization, DKIM-Signature assembly, and OpenSSL EVP signing
(cryptlib cannot emit a raw PKCS#1 signature). This is an OpenSSL-only feature, gated on pkg-config libcrypto; without it the entry points
compile to no-op stubs and mail goes out unsigned.

Integration in sendmail_thread uses a two-pass render: pass 1 captures
the message via a thread-local observer on sockprintf (nothing
transmitted) to compute the body hash and collect the signed headers,
then the DKIM-Signature is prepended and pass 2 transmits while
re-hashing the body, aborting on a mismatch. mimegetboundary() gains a
seed so both passes produce an identical MIME boundary; the MSG_KILLFILE attachment removal and the msg.subj mutation are guarded/saved so the
capture pass has no side effects. POP3 retrieval and the
DKIM-disabled path are byte-for-byte unchanged.

SCFG gains DKIM Signing / Domain / Selector options under Mail Server -> SendMail Support (scfgindex.h regenerated).

Live-validated on mail.synchro.net: Gmail reports dkim=pass, and
dmarc=pass for a *.synchro.net From address (relaxed alignment against a
single d=synchro.net key).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
(cherry picked from commit d28f2990942da53bfc96e3ed84daeac8277a41e1)

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