sendmail: from Vladimir:

Here comes the third part of compatibility patch for sendmail.
* Introduced new safe_getdomainname() -- will it be useful?
* Fixed SEGV if sender address is missed. Should snoop for sender address in mail headers?
* More compat: use HOSTNAME instead of HOST when no server is explicitly specified.
* crond: fixed mail recipient address.

function                                             old     new   delta
safe_getdomainname                                     -      56     +56
sendgetmail_main                                    1937    1946      +9
grep_file                                            846     850      +4
crond_main                                          1423    1425      +2
xstrtoull_range_sfx                                  295     296      +1
utoa_to_buf                                          110     108      -2
passwd_main                                         1053    1049      -4
sv_main                                             1234    1228      -6
parse_expr                                           841     833      -8
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/4 up/down: 72/-20)             Total: 52 bytes

4 files changed, 46 insertions, 25 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 7bc0dca..54601f8 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -630,6 +630,7 @@ void qsort_string_vector(char **sv, unsigned count) FAST_FUNC;
 int safe_poll(struct pollfd *ufds, nfds_t nfds, int timeout_ms) FAST_FUNC;
 
 char *safe_gethostname(void) FAST_FUNC;
+char *safe_getdomainname(void) FAST_FUNC;
 
 /* Convert each alpha char in str to lower-case */
 char* str_tolower(char *str) FAST_FUNC;
diff --git a/libbb/safe_gethostname.c b/libbb/safe_gethostname.c
index 1f8b2a8..7407fb7 100644
--- a/libbb/safe_gethostname.c
+++ b/libbb/safe_gethostname.c
@@ -48,6 +48,19 @@ char* FAST_FUNC safe_gethostname(void)
 
 	/* Uname can fail only if you pass a bad pointer to it. */
 	uname(&uts);
+	return xstrndup(!uts.nodename[0] ? "?" : uts.nodename, sizeof(uts.nodename));
+}
 
-	return xstrndup(!*(uts.nodename) ? "?" : uts.nodename, sizeof(uts.nodename));
+/*
+ * On success return the current malloced and NUL terminated domainname.
+ * On error return malloced and NUL terminated string "?".
+ * This is an illegal first character for a domainname.
+ * The returned malloced string must be freed by the caller.
+ */
+char* FAST_FUNC safe_getdomainname(void)
+{
+	struct utsname uts;
+
+	uname(&uts);
+	return xstrndup(!uts.domainname[0] ? "?" : uts.domainname, sizeof(uts.domainname));
 }
diff --git a/miscutils/crond.c b/miscutils/crond.c
index 27f24dd..51b09ec 100644
--- a/miscutils/crond.c
+++ b/miscutils/crond.c
@@ -839,7 +839,7 @@ static void RunJob(const char *user, CronLine *line)
 
 		if (mailFd >= 0) {
 			line->cl_MailFlag = 1;
-			fdprintf(mailFd, "To: %s\nSubject: cron: %s\n\n", user,
+			fdprintf(mailFd, "To: %s\nSubject: cron: %s\n\n", line->cl_MailTo,
 				line->cl_Shell);
 			line->cl_MailPos = lseek(mailFd, 0, SEEK_CUR);
 		} else {
diff --git a/networking/sendmail.c b/networking/sendmail.c
index b81c852..1c23ca2 100644
--- a/networking/sendmail.c
+++ b/networking/sendmail.c
@@ -305,6 +305,7 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 		OPTS_i = 1 << 7,        // sendmail: ignore lone dots in message body (implied)
 
 		OPTS_N = 1 << 8,        // sendmail: request notification
+		OPTS_f = 1 << 9,        // sendmail: sender address
 	};
 	const char *options;
 	int opts;
@@ -317,7 +318,7 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 	// and is NOT NULL if we are called as sendmail
 	if (!ENABLE_FETCHMAIL || 's' == applet_name[0]) {
 		// SENDMAIL
-		// save initial stdin (body or attachements can be piped!)
+		// save initial stdin since body is piped!
 		xdup2(STDIN_FILENO, INITIAL_STDIN_FILENO);
 		opt_complementary = "w+:a::";
 		options = "w:H:St" "s:c:a:iN:f:";
@@ -337,9 +338,9 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 	argv += optind;
 
 	// connect to server
-	// host[:port] not specified ? -> use $HOST. no $HOST ? -> use localhost
+	// host[:port] not specified ? -> use $HOSTNAME. no $HOSTNAME ? -> use localhost
 	if (!(opts & OPT_H)) {
-		opt_connect = getenv("HOST");
+		opt_connect = getenv("HOSTNAME");
 		if (!opt_connect)
 			opt_connect = "127.0.0.1";
 	}
@@ -349,6 +350,12 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 	opt_connect = parse_url((char*)opt_connect, &opt_user, &opt_pass);
 //	bb_error_msg("H[%s] U[%s] P[%s]", opt_connect, opt_user, opt_pass);
 
+	// username must be defined!
+	if (!opt_user) {
+		// N.B. IMHO getenv("USER") can be way easily spoofed!
+		opt_user = bb_getpwuid(NULL, -1, getuid());
+	}
+
 	// SSL ordered? ->
 	if (opts & OPT_S) {
 		// ... use openssl helper
@@ -384,12 +391,6 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 			argv++;
 		}
 
-		// we didn't use SSL helper? ->
-		if (!(opts & OPT_S)) {
-			// ... wait for initial server OK
-			smtp_check(NULL, 220);
-		}
-
 		// if -t specified or no recipients specified -> enter all-included mode
 		// i.e. scan stdin for To: and Subject: lines ...
 		// ... and then use the rest of stdin as message body
@@ -402,7 +403,10 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 			while ((s = xmalloc_reads(INITIAL_STDIN_FILENO, NULL, NULL)) != NULL) {
 				if (0 == strncmp("To: ", s, 4)) {
 					llist_add_to_end(&opt_recipients, s+4);
-				} else if (0 == strncmp("Subject: ", s, 9)) {
+/*				} else if (0 == strncmp("From: ", s, 6)) {
+					opt_from = s+6;
+					opts |= OPTS_f;
+*/				} else if (0 == strncmp("Subject: ", s, 9)) {
 					opt_subject = s+9;
 					opts |= OPTS_s;
 				} else {
@@ -414,7 +418,21 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 			}
 		}
 
+		// got no sender address? -> use username as a resort
+		if (!(opts & OPTS_f)) {
+			char *domain = safe_getdomainname();
+			opt_from = xasprintf("%s@%s", opt_user, domain);
+			free(domain);
+		}
+
 		// introduce to server
+
+		// we didn't use SSL helper? ->
+		if (!(opts & OPT_S)) {
+			// ... wait for initial server OK
+			smtp_check(NULL, 220);
+		}
+
 		// we should start with modern EHLO
 		if (250 != smtp_checkp("EHLO %s", sane(opt_from), -1)) {
 			smtp_checkp("HELO %s", opt_from, 250);
@@ -427,16 +445,8 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 		// first try softly without authentication
 		while (250 != smtp_checkp("MAIL FROM:<%s>", opt_from, code)) {
 			// MAIL FROM failed -> authentication needed
-			// have we got username?
-			if (!opt_user) {
-				// no! fetch it from "from" option
-				opt_user = xstrdup(opt_from);
-				*strchrnul(opt_user, '@') = '\0';
-			}
-			// now we've got username
-			// so try to authenticate
 			if (334 == smtp_check("AUTH LOGIN", -1)) {
-				uuencode(NULL, opt_user);
+				uuencode(NULL, opt_user); // opt_user != NULL
 				smtp_check("", 334);
 				uuencode(NULL, opt_pass);
 				smtp_check("", 235);
@@ -552,10 +562,7 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 		*fargs = *argv;
 
 		// authenticate
-		if (!opt_user) {
-			// N.B. IMHO getenv("USER") can be way easily spoofed!
-			opt_user = bb_getpwuid(NULL, -1, getuid());
-		}
+
 		// password is mandatory
 		if (!opt_pass) {
 			bb_error_msg_and_die("no password");