--- head.c	2006-03-04 00:32:16.000000000 +0000
+++ head.c	2021-11-29 21:35:12.043385175 +0000
@@ -1116,10 +1116,8 @@
 	if ((t = combinetime(year, month, day, hour, minute, second)) ==
 			(time_t)-1)
 		goto invalid;
-	tzdiff = t - mktime(gmtime(&t));
 	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff += 3600;
+	tzdiff = tmptr->tm_gmtoff; /* seconds east of GMT */
 	t -= tzdiff;
 	return t;
 invalid:
--- imap.c	2009-03-13 15:39:15.000000000 +0000
+++ imap.c	2021-11-29 21:29:26.885202809 +0000
@@ -3530,10 +3530,8 @@
 		return -1;
 	if ((t = combinetime(year, month, day, 0, 0, 0)) == (time_t)-1)
 		return -1;
-	tzdiff = t - mktime(gmtime(&t));
 	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff += 3600;
+	tzdiff = tmptr->tm_gmtoff; /* seconds east of GMT */
 	t -= tzdiff;
 	return t;
 }
@@ -3545,13 +3543,11 @@
 	struct tm	*tmptr;
 	int	tzdiff, tzdiff_hour, tzdiff_min;
 
-	tzdiff = t - mktime(gmtime(&t));
+	tmptr = localtime(&t);
+	tzdiff = tmptr->tm_gmtoff; /* seconds east of GMT */
 	tzdiff_hour = (int)(tzdiff / 60);
 	tzdiff_min = tzdiff_hour % 60;
 	tzdiff_hour /= 60;
-	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff_hour++;
 	snprintf(s, sizeof s, "\"%02d-%s-%04d %02d:%02d:%02d %+03d%02d\"",
 			tmptr->tm_mday,
 			month_names[tmptr->tm_mon],
--- sendout.c	2009-03-01 20:25:42.000000000 +0000
+++ sendout.c	2021-11-29 19:35:39.421305295 +0000
@@ -1123,9 +1123,7 @@
 
 /*
  * Create a Date: header field.
- * We compare the localtime() and gmtime() results to get the timezone,
- * because numeric timezones are easier to read and because $TZ is
- * not set on most GNU systems.
+ * We use tm->tm_gmtoff to account for negative DST adjustments (e.g. Ireland).
  */
 int
 mkdate(FILE *fo, const char *field)
@@ -1135,13 +1133,11 @@
 	int tzdiff, tzdiff_hour, tzdiff_min;
 
 	time(&t);
-	tzdiff = t - mktime(gmtime(&t));
+	tmptr = localtime(&t);
+	tzdiff = tmptr->tm_gmtoff; /* seconds east of GMT */
 	tzdiff_hour = (int)(tzdiff / 60);
 	tzdiff_min = tzdiff_hour % 60;
 	tzdiff_hour /= 60;
-	tmptr = localtime(&t);
-	if (tmptr->tm_isdst > 0)
-		tzdiff_hour++;
 	return fprintf(fo, "%s: %s, %02d %s %04d %02d:%02d:%02d %+05d\n",
 			field,
 			weekday_names[tmptr->tm_wday],