diff -r f8f63e944375 sys/src/cmd/upas/common/common.h
--- a/sys/src/cmd/upas/common/common.h	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/common/common.h	Sat Jul 18 23:30:43 2020 -0700
@@ -52,9 +52,6 @@
 void	mailfmtinstall(void);	/* 'U' = 2047fmt */
 #pragma varargck	type	"U"	char*
 
-/* totm.c */
-int	fromtotm(char*, Tm*);
-
 /* a pipe between parent and child*/
 typedef struct{
 	Biobuf	bb;
diff -r f8f63e944375 sys/src/cmd/upas/common/folder.c
--- a/sys/src/cmd/upas/common/folder.c	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/common/folder.c	Sat Jul 18 23:30:43 2020 -0700
@@ -1,5 +1,7 @@
 #include "common.h"
 
+#define Ctimefmt "W MMM _D hh:mm:ss ZZZ YYYY"
+
 enum{
 	Mbox	= 1,
 	Mdir,
@@ -185,7 +187,7 @@
 appendfolder(Biobuf *b, char *addr, int fd)
 {
 	char *s;
-	int r;
+	int r, n;
 	Biobuf bin;
 	Folder *f;
 	Tm tm;
@@ -194,9 +196,10 @@
 	Bseek(f->out, 0, 2);
 	Binit(&bin, fd, OREAD);
 	s = Brdstr(&bin, '\n', 0);
-	if(!s || strncmp(s, "From ", 5))
+	n = strlen(s);
+	if(!s || strncmp(s, "From ", 5) != 0)
 		Bprint(f->out, "From %s %.28s\n", addr, ctime(f->t));
-	else if(fromtotm(s, &tm) >= 0)
+	else if(n > 5 && tmparse(&tm, Ctimefmt, s + 5, nil, nil) != nil)
 		f->t = tm2sec(&tm);
 	if(s)
 		Bwrite(f->out, s, strlen(s));
diff -r f8f63e944375 sys/src/cmd/upas/common/mkfile
--- a/sys/src/cmd/upas/common/mkfile	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/common/mkfile	Sat Jul 18 23:30:43 2020 -0700
@@ -10,7 +10,6 @@
 	fmt.$O\
 	libsys.$O\
 	process.$O\
-	totm.$O\
 
 HFILES=common.h\
 	sys.h\
diff -r f8f63e944375 sys/src/cmd/upas/common/totm.c
--- a/sys/src/cmd/upas/common/totm.c	Fri Jul 17 16:53:20 2020 +0200
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,36 +0,0 @@
-#include <common.h>
-
-static char mtab[] = "JanFebMarAprMayJunJulAugSepOctNovDec";
-
-int
-ctimetotm(char *s, Tm *tm)
-{
-	char buf[32];
-
-	if(strlen(s) < 28)
-		return -1;
-	snprint(buf, sizeof buf, "%s", s);
-	memset(tm, 0, sizeof *tm);
-	buf[7] = 0;
-	tm->mon = (strstr(mtab, buf+4) - mtab)/3;
-	tm->mday = atoi(buf+8);
-	tm->hour = atoi(buf+11);
-	tm->min = atoi(buf+14);
-	tm->sec = atoi(buf+17);
-	tm->zone[0] = buf[20];
-	tm->zone[1] = buf[21];
-	tm->zone[2] = buf[22];
-	tm->year = atoi(buf+24) - 1900;
-	return 0;
-}
-
-int
-fromtotm(char *s, Tm *tm)
-{
-	char buf[256], *f[3];
-
-	snprint(buf, sizeof buf, "%s", s);
-	if(getfields(buf, f, nelem(f), 0, " ") != 3)
-		return -1;
-	return ctimetotm(f[2], tm);
-}
diff -r f8f63e944375 sys/src/cmd/upas/fs/strtotm.c
--- a/sys/src/cmd/upas/fs/strtotm.c	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/fs/strtotm.c	Sat Jul 18 23:30:43 2020 -0700
@@ -1,98 +1,25 @@
 #include <u.h>
 #include <libc.h>
 
-static char*
-skiptext(char *q)
+int
+strtotm(char *s, Tm *t)
 {
-	while(*q != '\0' && *q != ' ' && *q != '\t' && *q != '\r' && *q != '\n')
-		q++;
-	return q;
+	char **f, *fmt[] = {
+		"W MMM DD hh:mm:ss ?Z YYYY",
+		"?W ?DD ?MMM ?YYYY hh:mm:ss ?Z",
+		"?W ?DD ?MMM ?YYYY hh:mm:ss",
+		"?W, DD-?MM-YY",
+		"?DD ?MMM ?YYYY hh:mm:ss ?Z",
+		"?DD ?MMM ?YYYY hh:mm:ss",
+		"?DD-?MM-YY",
+		"?MMM/?DD/?YYYY hh:mm:ss ?Z",
+		"?MMM/?DD/?YYYY hh:mm:ss",
+		"?MMM/?DD/?YYYY",
+		nil,
+	};
+
+	for(f = fmt; *f; f++)
+		if(tmparse(t, *f, s, nil, nil) != nil)
+			return 0;
+	return -1;
 }
-
-static char*
-skipwhite(char *q)
-{
-	while(*q == ' ' || *q == '\t' || *q == '\r' || *q == '\n')
-		q++;
-	return q;
-}
-
-static char* months[] = {
-	"jan", "feb", "mar", "apr",
-	"may", "jun", "jul", "aug",
-	"sep", "oct", "nov", "dec"
-};
-
-int
-strtotm(char *p, Tm *t)
-{
-	char *q, *r;
-	int j;
-	Tm tm;
-	int delta;
-
-	delta = 0;
-	memset(&tm, 0, sizeof(tm));
-	tm.mon = -1;
-	tm.hour = -1;
-	tm.min = -1;
-	tm.year = -1;
-	tm.mday = -1;
-	memcpy(tm.zone, "GMT", 3);
-	for(p = skipwhite(p); *p; p = skipwhite(q)){
-		q = skiptext(p);
-
-		/* look for time in hh:mm[:ss] */
-		if(r = memchr(p, ':', q - p)){
-			tm.hour = strtol(p, 0, 10);
-			tm.min = strtol(r + 1, 0, 10);
-			if(r = memchr(r + 1, ':', q - (r + 1)))
-				tm.sec = strtol(r + 1, 0, 10);
-			else
-				tm.sec = 0;
-			continue;
-		}
-
-		/* look for month */
-		for(j = 0; j < 12; j++)
-			if(cistrncmp(p, months[j], 3) == 0){
-				tm.mon = j;
-				break;
-			}
-		if(j != 12)
-			continue;
-
-		/* look for time zone [A-Z][A-Z]T */
-		if(q - p == 3)
-		if(p[0] >= 'A' && p[0] <= 'Z')
-		if(p[1] >= 'A' && p[1] <= 'Z')
-		if(p[2] == 'T'){
-			strecpy(tm.zone, tm.zone + 4, p);
-			continue;
-		}
-
-		if(p[0] == '+'||p[0] == '-')
-		if(q - p == 5 && strspn(p + 1, "0123456789") == 4){
-			delta = (((p[1] - '0')*10 + p[2] - '0')*60 + (p[3] - '0')*10 + p[4] - '0')*60;
-			if(p[0] == '-')
-				delta = -delta;
-			continue;
-		}
-		if(strspn(p, "0123456789") == q - p){
-			j = strtol(p, nil, 10);
-			if(j >= 1 && j <= 31)
-				tm.mday = j;
-			if(j >= 1900)
-				tm.year = j - 1900;
-			continue;
-		}
-		//eprint("strtotm: garbage %.*s\n", utfnlen(p, q - p), p);
-	}
-	if(tm.mon < 0 || tm.year < 0
-	|| tm.hour < 0 || tm.min < 0
-	|| tm.mday < 0)
-		return -1;
-
-	*t = *localtime(tm2sec(&tm) - delta);
-	return 0;
-}
diff -r f8f63e944375 sys/src/cmd/upas/imap4d/date.c
--- a/sys/src/cmd/upas/imap4d/date.c	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/imap4d/date.c	Sat Jul 18 23:30:43 2020 -0700
@@ -1,142 +1,10 @@
 #include "imap4d.h"
 
-static char *wdayname[] = {
-	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
-};
-
-static char *monname[] = {
-	"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
-};
-
-/*
- * zone	: [A-Za-z][A-Za-z][A-Za-z]	some time zone names
- *	| [A-IK-Z]			military time; rfc1123 says the rfc822 spec is wrong.
- *	| "UT"				universal time
- *	| [+-][0-9][0-9][0-9][0-9]
- * zones is the rfc-822 list of time zone names
- */
-static Namedint zones[] =
-{
-	{"A",	-1 * 3600},
-	{"B",	-2 * 3600},
-	{"C",	-3 * 3600},
-	{"CDT", -5 * 3600},
-	{"CST", -6 * 3600},
-	{"D",	-4 * 3600},
-	{"E",	-5 * 3600},
-	{"EDT", -4 * 3600},
-	{"EST", -5 * 3600},
-	{"F",	-6 * 3600},
-	{"G",	-7 * 3600},
-	{"GMT", 0},
-	{"H",	-8 * 3600},
-	{"I",	-9 * 3600},
-	{"K",	-10 * 3600},
-	{"L",	-11 * 3600},
-	{"M",	-12 * 3600},
-	{"MDT", -6 * 3600},
-	{"MST", -7 * 3600},
-	{"N",	+1 * 3600},
-	{"O",	+2 * 3600},
-	{"P",	+3 * 3600},
-	{"PDT", -7 * 3600},
-	{"PST", -8 * 3600},
-	{"Q",	+4 * 3600},
-	{"R",	+5 * 3600},
-	{"S",	+6 * 3600},
-	{"T",	+7 * 3600},
-	{"U",	+8 * 3600},
-	{"UT",	0},
-	{"V",	+9 * 3600},
-	{"W",	+10 * 3600},
-	{"X",	+11 * 3600},
-	{"Y",	+12 * 3600},
-	{"Z",	0},
-};
-
-static void
-zone2tm(Tm *tm, char *s)
-{
-	int i;
-	Tm aux, *atm;
-
-	if(*s == '+' || *s == '-'){
-		i = strtol(s, &s, 10);
-		tm->tzoff = (i/100)*3600 + i%100;
-		strncpy(tm->zone, "", 4);
-		return;
-	}
-
-	/*
-	 * look it up in the standard rfc822 table
-	 */
-	strncpy(tm->zone, s, 3);
-	tm->zone[3] = 0;
-	tm->tzoff = 0;
-	for(i = 0; i < nelem(zones); i++){
-		if(cistrcmp(zones[i].name, s) == 0){
-			tm->tzoff = zones[i].v;
-			return;
-		}
-	}
-
-	/*
-	 * one last try: look it up in the current local timezone
-	 * probe a couple of times to get daylight/standard time change.
-	 */
-	aux = *tm;
-	memset(aux.zone, 0, 4);
-	aux.hour--;
-	for(i = 0; i < 2; i++){
-		atm = localtime(tm2sec(&aux));
-		if(cistrcmp(tm->zone, atm->zone) == 0){
-			tm->tzoff = atm->tzoff;
-			return;
-		}
-		aux.hour++;
-	}
-
-	strncpy(tm->zone, "GMT", 4);
-	tm->tzoff = 0;
-}
-
-/*
- * hh[:mm[:ss]]
- */
-static void
-time2tm(Tm *tm, char *s)
-{
-	tm->hour = strtoul(s, &s, 10);
-	if(*s++ != ':')
-		return;
-	tm->min = strtoul(s, &s, 10);
-	if(*s++ != ':')
-		return;
-	tm->sec = strtoul(s, &s, 10);
-}
-
-static int
-dateindex(char *d, char **tab, int n)
-{
-	int i;
-
-	for(i = 0; i < n; i++)
-		if(cistrcmp(d, tab[i]) == 0)
-			return i;
-	return -1;
-}
-
 int
 imap4date(Tm *tm, char *date)
 {
-	char *flds[4];
-
-	if(getfields(date, flds, 3, 0, "-") != 3)
+	if(tmparse(tm, "DD-?MM-YYYY hh:mm:ss ?Z", date, nil, nil) == nil)
 		return 0;
-
-	tm->mday = strtol(flds[0], nil, 10);
-	tm->mon = dateindex(flds[1], monname, 12);
-	tm->year = strtol(flds[2], nil, 10) - 1900;
 	return 1;
 }
 
@@ -146,29 +14,17 @@
 ulong
 imap4datetime(char *date)
 {
-	char *flds[4], *sflds[4];
-	ulong t;
 	Tm tm;
+	vlong s;
 
-	if(getfields(date, flds, 4, 0, " ") != 3)
-		return ~0;
-
-	if(!imap4date(&tm, flds[0]))
-		return ~0;
-
-	if(getfields(flds[1], sflds, 3, 0, ":") != 3)
-		return ~0;
-
-	tm.hour = strtol(sflds[0], nil, 10);
-	tm.min = strtol(sflds[1], nil, 10);
-	tm.sec = strtol(sflds[2], nil, 10);
-
-	strcpy(tm.zone, "GMT");
-	tm.yday = 0;
-	t = tm2sec(&tm);
-	zone2tm(&tm, flds[2]);
-	t -= tm.tzoff;
-	return t;
+	s = -1;
+	if(tmparse(&tm, "?DD-?MM-YYYY hh:mm:ss ?Z", date, nil, nil) != nil)
+		s = tmnorm(&tm);
+	else if(tmparse(&tm, "?W, ?DD-?MM-YYYY hh:mm:ss ?Z", date, nil, nil) != nil)
+		s = tmnorm(&tm);
+	if(s > 0 && s < (1ULL<<31))
+		return s;
+	return ~0;
 }
 
 /*
@@ -181,85 +37,18 @@
 Tm*
 date2tm(Tm *tm, char *date)
 {
-	char *flds[7], *s, dstr[64];
-	int n;
-	Tm gmt, *atm;
+	char **f, *fmts[] = {
+		"?W, ?DD ?MMM YYYY hh:mm:ss ?Z",
+		"?W ?M ?DD hh:mm:ss ?Z YYYY",
+		"?W, DD-?MM-YY hh:mm:ss ?Z",
+		"?DD ?MMM YYYY hh:mm:ss ?Z",
+		"?M ?DD hh:mm:ss ?Z YYYY",
+		"DD-?MM-YYYY hh:mm:ss ?Z",
+		nil,
+	};
 
-	/*
-	 * default date is Thu Jan  1 00:00:00 GMT 1970
-	 */
-	tm->wday = 4;
-	tm->mday = 1;
-	tm->mon = 1;
-	tm->hour = 0;
-	tm->min = 0;
-	tm->sec = 0;
-	tm->year = 70;
-	strcpy(tm->zone, "GMT");
-	tm->tzoff = 0;
-
-	strncpy(dstr, date, sizeof dstr);
-	dstr[sizeof dstr - 1] = 0;
-	n = tokenize(dstr, flds, 7);
-	if(n != 6 && n != 5)
-		return nil;
-
-	if(n == 5){
-		for(n = 5; n >= 1; n--)
-			flds[n] = flds[n - 1];
-		n = 5;
-	}else{
-		/*
-		 * Wday[,]
-		 */
-		s = strchr(flds[0], ',');
-		if(s != nil)
-			*s = 0;
-		tm->wday = dateindex(flds[0], wdayname, 7);
-		if(tm->wday < 0)
-			return nil;
-	}
-
-	/*
-	 * check for the two major formats:
-	 * Month first or day first
-	 */
-	tm->mon = dateindex(flds[1], monname, 12);
-	if(tm->mon >= 0){
-		tm->mday = strtoul(flds[2], nil, 10);
-		time2tm(tm, flds[3]);
-		zone2tm(tm, flds[4]);
-		tm->year = strtoul(flds[5], nil, 10);
-		if(strlen(flds[5]) > 2)
-			tm->year -= 1900;
-	}else{
-		tm->mday = strtoul(flds[1], nil, 10);
-		tm->mon = dateindex(flds[2], monname, 12);
-		if(tm->mon < 0)
-			return nil;
-		tm->year = strtoul(flds[3], nil, 10);
-		if(strlen(flds[3]) > 2)
-			tm->year -= 1900;
-		time2tm(tm, flds[4]);
-		zone2tm(tm, flds[5]);
-	}
-
-	if(n == 5){
-		gmt = *tm;
-		strncpy(gmt.zone, "", 4);
-		gmt.tzoff = 0;
-		atm = gmtime(tm2sec(&gmt));
-		tm->wday = atm->wday;
-	}else{
-		/*
-		 * Wday[,]
-		 */
-		s = strchr(flds[0], ',');
-		if(s != nil)
-			*s = 0;
-		tm->wday = dateindex(flds[0], wdayname, 7);
-		if(tm->wday < 0)
-			return nil;
-	}
-	return tm;
+	for(f = fmts; *f; f++)
+		if(tmparse(tm, *f, date, nil, nil) != nil)
+			return tm;
+	return nil;
 }
diff -r f8f63e944375 sys/src/cmd/upas/imap4d/imap4d.c
--- a/sys/src/cmd/upas/imap4d/imap4d.c	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/imap4d/imap4d.c	Sat Jul 18 23:30:43 2020 -0700
@@ -215,6 +215,7 @@
 	Binit(&bin, dup(0, -1), OREAD);
 	close(0);
 	Binit(&bout, 1, OWRITE);
+	tmfmtinstall();
 	quotefmtinstall();
 	fmtinstall('F', Ffmt);
 	fmtinstall('D', Dfmt);	/* rfc822; # imap date %Z */
diff -r f8f63e944375 sys/src/cmd/upas/imap4d/print.c
--- a/sys/src/cmd/upas/imap4d/print.c	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/imap4d/print.c	Sat Jul 18 23:30:43 2020 -0700
@@ -90,40 +90,24 @@
 	return fmtstrcpy(f, encfs(buf, sizeof buf, s));
 }
 
-static char *day[] = {
-	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
-};
-
-static char *mon[] = {
-	"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
-};
-
 int
 Dfmt(Fmt *f)
 {
-	char buf[128], *p, *e, *sgn, *fmt;
-	int off;
-	Tm *tm;
+	char buf[128], *fmt;
+	Tm *tm, t;
 
 	tm = va_arg(f->args, Tm*);
-	if(tm == nil)
-		tm = localtime(time(0));
-	sgn = "+";
-	if(tm->tzoff < 0)
-		sgn = "";
-	e = buf + sizeof buf;
-	p = buf;
-	off = (tm->tzoff/3600)*100 + (tm->tzoff/60)%60;
+	if(tm == nil){
+		tz = tzload("local");
+		tm = tmtime(&t, time(0), tz);
+	}
 	if((f->flags & FmtSharp) == 0){
 		/* rfc822 style */
-		fmt = "%.2d %s %.4d %.2d:%.2d:%.2d %s%.4d";
-		p = seprint(p, e, "%s, ", day[tm->wday]);
+		fmt = "WW, DD MMM YYYY hh:mm:ss Z";
 	}else
-		fmt = "%2d-%s-%.4d %2.2d:%2.2d:%2.2d %s%4.4d";
-	seprint(p, e, fmt,
-		tm->mday, mon[tm->mon], tm->year + 1900, tm->hour, tm->min, tm->sec,
-		sgn, off);
+		fmt = "DD-MMM-YYYY hh:mm:ss Z";
 	if(f->r == L'δ')
-		return fmtstrcpy(f, buf);
+		return fmtprint(f, "%τ", tmfmt(tm, fmt));
+	snprint(buf, sizeof(buf), "%τ", tmfmt(tm, fmt));
 	return fmtprint(f, "%Z", buf);
 }
diff -r f8f63e944375 sys/src/cmd/upas/marshal/marshal.c
--- a/sys/src/cmd/upas/marshal/marshal.c	Fri Jul 17 16:53:20 2020 +0200
+++ b/sys/src/cmd/upas/marshal/marshal.c	Sat Jul 18 23:30:43 2020 -0700
@@ -140,6 +140,7 @@
 char lastchar;
 char *replymsg;
 
+#define Rfc822fmt	"WW, DD MMM YYYY hh:mm:ss Z"
 enum
 {
 	Ok = 0,
@@ -208,6 +209,7 @@
 	hdrstring = nil;
 	ccargc = bccargc = 0;
 
+	tmfmtinstall();
 	quotefmtinstall();
 	fmtinstall('Z', doublequote);
 	fmtinstall('U', rfc2047fmt);
@@ -792,29 +794,13 @@
 	Bterm(f);
 }
 
-char *ascwday[] =
-{
-	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
-};
-
-char *ascmon[] =
-{
-	"Jan", "Feb", "Mar", "Apr", "May", "Jun",
-	"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
-};
-
 int
 printdate(Biobuf *b)
 {
-	int tz;
 	Tm *tm;
 
 	tm = localtime(time(0));
-	tz = (tm->tzoff/3600)*100 + (tm->tzoff/60)%60;
-
-	return Bprint(b, "Date: %s, %d %s %d %2.2d:%2.2d:%2.2d %s%.4d\n",
-		ascwday[tm->wday], tm->mday, ascmon[tm->mon], 1900 + tm->year,
-		tm->hour, tm->min, tm->sec, tz>=0?"+":"", tz);
+	return Bprint(b, "Date: %τ\n", tmfmt(tm, Rfc822fmt));
 }
 
 int
@@ -1003,16 +989,10 @@
 int
 printunixfrom(int fd)
 {
-	int tz;
 	Tm *tm;
 
 	tm = localtime(time(0));
-	tz = (tm->tzoff/3600)*100 + (tm->tzoff/60)%60;
-
-	return fprint(fd, "From %s %s %s %d %2.2d:%2.2d:%2.2d %s%.4d %d\n",
-		user,
-		ascwday[tm->wday], ascmon[tm->mon], tm->mday,
-		tm->hour, tm->min, tm->sec, tz>=0?"+":"", tz, 1900 + tm->year);
+	return fprint(fd, "From %s %τ\n", user, tmfmt(tm, Rfc822fmt));
 }
 
 char *specialfile[] =