diff --git a/Documentation/git-commit-tree.txt b/Documentation/git-commit-tree.txt
index f524d76019..9ac30a3274 100644
--- a/Documentation/git-commit-tree.txt
+++ b/Documentation/git-commit-tree.txt
@@ -67,7 +67,9 @@ if set:
 
 In case (some of) these environment variables are not set, the information
 is taken from the configuration items user.name and user.email, or, if not
-present, system user name and fully qualified hostname.
+present, system user name and the hostname used for outgoing mail (taken
+from `/etc/mailname` and falling back to the fully qualified hostname when
+that file does not exist).
 
 A commit comment is read from stdin. If a changelog
 entry is not provided via "<" redirection, 'git commit-tree' will just wait
@@ -89,6 +91,10 @@ Discussion
 
 include::i18n.txt[]
 
+FILES
+-----
+/etc/mailname
+
 SEE ALSO
 --------
 linkgit:git-write-tree[1]
diff --git a/ident.c b/ident.c
index 35a6f26473..edb4314494 100644
--- a/ident.c
+++ b/ident.c
@@ -50,6 +50,54 @@ static void copy_gecos(const struct passwd *w, char *name, size_t sz)
 
 }
 
+static int add_mailname_host(char *buf, size_t len)
+{
+	FILE *mailname;
+
+	mailname = fopen("/etc/mailname", "r");
+	if (!mailname) {
+		if (errno != ENOENT)
+			warning("cannot open /etc/mailname: %s",
+				strerror(errno));
+		return -1;
+	}
+	if (!fgets(buf, len, mailname)) {
+		if (ferror(mailname))
+			warning("cannot read /etc/mailname: %s",
+				strerror(errno));
+		fclose(mailname);
+		return -1;
+	}
+	/* success! */
+	fclose(mailname);
+	return 0;
+}
+
+static void add_domainname(char *buf, size_t len)
+{
+	struct hostent *he;
+	size_t namelen;
+	const char *domainname;
+
+	if (gethostname(buf, len)) {
+		warning("cannot get host name: %s", strerror(errno));
+		strlcpy(buf, "(none)", len);
+		return;
+	}
+	namelen = strlen(buf);
+	if (memchr(buf, '.', namelen))
+		return;
+
+	he = gethostbyname(buf);
+	buf[namelen++] = '.';
+	buf += namelen;
+	len -= namelen;
+	if (he && (domainname = strchr(he->h_name, '.')))
+		strlcpy(buf, domainname + 1, len);
+	else
+		strlcpy(buf, "(none)", len);
+}
+
 static void copy_email(const struct passwd *pw)
 {
 	/*
@@ -61,20 +109,12 @@ static void copy_email(const struct passwd *pw)
 		die("Your sysadmin must hate you!");
 	memcpy(git_default_email, pw->pw_name, len);
 	git_default_email[len++] = '@';
-	gethostname(git_default_email + len, sizeof(git_default_email) - len);
-	if (!strchr(git_default_email+len, '.')) {
-		struct hostent *he = gethostbyname(git_default_email + len);
-		char *domainname;
 
-		len = strlen(git_default_email);
-		git_default_email[len++] = '.';
-		if (he && (domainname = strchr(he->h_name, '.')))
-			strlcpy(git_default_email + len, domainname + 1,
-				sizeof(git_default_email) - len);
-		else
-			strlcpy(git_default_email + len, "(none)",
-				sizeof(git_default_email) - len);
-	}
+	if (!add_mailname_host(git_default_email + len,
+				sizeof(git_default_email) - len))
+		return;	/* read from "/etc/mailname" (Debian) */
+	add_domainname(git_default_email + len,
+			sizeof(git_default_email) - len);
 }
 
 static void setup_ident(void)