diff --git a/config/config.go b/config/config.go
index 9754e1d..1302010 100644
--- a/config/config.go
+++ b/config/config.go
@@ -4,10 +4,12 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
+	"github.com/robfig/cron/v3"
 	"io/ioutil"
 	"net/http"
 	"os"
 	"regexp"
+	"strconv"
 	"strings"
 	"time"
 
@@ -242,13 +244,81 @@ func (c *appConfig) GetOSColors() map[string]string {
 	return cloneStringMap(c.Colors["operating_systems"], true)
 }
 
-func (c *appConfig) GetWeeklyReportDay() time.Weekday {
-	s := strings.Split(c.ReportTimeWeekly, ",")[0]
-	return parseWeekday(s)
+func (c *appConfig) GetAggregationTimeCron() string {
+	if strings.Contains(c.AggregationTime, ":") {
+		// old format, e.g. "15:04"
+		timeParts := strings.Split(c.AggregationTime, ":")
+		h, err := strconv.Atoi(timeParts[0])
+		if err != nil {
+			logbuch.Fatal(err.Error())
+		}
+
+		m, err := strconv.Atoi(timeParts[1])
+		if err != nil {
+			logbuch.Fatal(err.Error())
+		}
+
+		return fmt.Sprintf("0 %d %d * * *", m, h)
+	}
+
+	return cronPadToSecondly(c.AggregationTime)
 }
 
-func (c *appConfig) GetWeeklyReportTime() string {
-	return strings.Split(c.ReportTimeWeekly, ",")[1]
+func (c *appConfig) GetWeeklyReportCron() string {
+	if strings.Contains(c.ReportTimeWeekly, ",") {
+		// old format, e.g. "fri,18:00"
+		split := strings.Split(c.ReportTimeWeekly, ",")
+		weekday := parseWeekday(split[0])
+		timeParts := strings.Split(split[1], ":")
+
+		h, err := strconv.Atoi(timeParts[0])
+		if err != nil {
+			logbuch.Fatal(err.Error())
+		}
+
+		m, err := strconv.Atoi(timeParts[1])
+		if err != nil {
+			logbuch.Fatal(err.Error())
+		}
+
+		return fmt.Sprintf("0 %d %d * * %d", m, h, weekday)
+	}
+
+	return cronPadToSecondly(c.ReportTimeWeekly)
+}
+
+func (c *appConfig) GetLeaderboardGenerationTimeCron() []string {
+	crons := []string{}
+
+	var parse func(string) string
+
+	if strings.Contains(c.LeaderboardGenerationTime, ":") {
+		// old format, e.g. "15:04"
+		parse = func(s string) string {
+			timeParts := strings.Split(s, ":")
+			h, err := strconv.Atoi(timeParts[0])
+			if err != nil {
+				logbuch.Fatal(err.Error())
+			}
+
+			m, err := strconv.Atoi(timeParts[1])
+			if err != nil {
+				logbuch.Fatal(err.Error())
+			}
+
+			return fmt.Sprintf("0 %d %d * * *", m, h)
+		}
+	} else {
+		parse = func(s string) string {
+			return cronPadToSecondly(s)
+		}
+	}
+
+	for _, s := range strings.Split(c.LeaderboardGenerationTime, ";") {
+		crons = append(crons, parse(strings.TrimSpace(s)))
+	}
+
+	return crons
 }
 
 func (c *appConfig) HeartbeatsMaxAge() time.Duration {
@@ -352,6 +422,14 @@ func parseWeekday(s string) time.Weekday {
 	return time.Monday
 }
 
+func cronPadToSecondly(expr string) string {
+	parts := strings.Split(expr, " ")
+	if len(parts) == 6 {
+		return expr
+	}
+	return "0 " + expr
+}
+
 func Set(config *Config) {
 	cfg = config
 }
@@ -414,16 +492,35 @@ func Load(version string) *Config {
 	if config.Mail.Provider != "" && findString(config.Mail.Provider, emailProviders, "") == "" {
 		logbuch.Fatal("unknown mail provider '%s'", config.Mail.Provider)
 	}
-	if _, err := time.Parse("15:04", config.App.GetWeeklyReportTime()); err != nil {
-		logbuch.Fatal("invalid interval set for report_time_weekly")
-	}
-	if _, err := time.Parse("15:04", config.App.AggregationTime); err != nil {
-		logbuch.Fatal("invalid interval set for aggregation_time")
-	}
 	if _, err := time.ParseDuration(config.App.HeartbeatMaxAge); err != nil {
 		logbuch.Fatal("invalid duration set for heartbeat_max_age")
 	}
 
+	cronParser := cron.NewParser(cron.Second | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor)
+
+	if _, err := cronParser.Parse(config.App.GetWeeklyReportCron()); err != nil {
+		logbuch.Fatal("invalid cron expression for report_time_weekly")
+	}
+	if _, err := cronParser.Parse(config.App.GetAggregationTimeCron()); err != nil {
+		logbuch.Fatal("invalid cron expression for aggregation_time")
+	}
+	for _, c := range config.App.GetLeaderboardGenerationTimeCron() {
+		if _, err := cronParser.Parse(c); err != nil {
+			logbuch.Fatal("invalid cron expression for leaderboard_generation_time")
+		}
+	}
+
+	// deprecation notices
+	if strings.Contains(config.App.AggregationTime, ":") {
+		logbuch.Warn("you're using deprecated syntax for 'aggregation_time', please change it to a valid cron expression")
+	}
+	if strings.Contains(config.App.ReportTimeWeekly, ":") {
+		logbuch.Warn("you're using deprecated syntax for 'report_time_weekly', please change it to a valid cron expression")
+	}
+	if strings.Contains(config.App.LeaderboardGenerationTime, ":") {
+		logbuch.Warn("you're using deprecated syntax for 'leaderboard_generation_time', please change it to a semicolon-separated list if valid cron expressions")
+	}
+
 	Set(config)
 	return Get()
 }
diff --git a/config/jobqueue.go b/config/jobqueue.go
new file mode 100644
index 0000000..baf3c0d
--- /dev/null
+++ b/config/jobqueue.go
@@ -0,0 +1,44 @@
+package config
+
+import (
+	"fmt"
+	"github.com/muety/artifex"
+)
+
+var jobqueues map[string]*artifex.Dispatcher
+
+const (
+	QueueDefault    = ""
+	QueueProcessing = "processing"
+	QueueMails      = "mails"
+)
+
+func init() {
+	jobqueues = make(map[string]*artifex.Dispatcher)
+}
+
+func InitQueue(name string, workers int) error {
+	if _, ok := jobqueues[name]; ok {
+		return fmt.Errorf("queue '%s' already existing", name)
+	}
+	jobqueues[name] = artifex.NewDispatcher(workers, 4096)
+	jobqueues[name].Start()
+	return nil
+}
+
+func GetDefaultQueue() *artifex.Dispatcher {
+	return GetQueue("")
+}
+
+func GetQueue(name string) *artifex.Dispatcher {
+	if _, ok := jobqueues[name]; !ok {
+		InitQueue(name, 1)
+	}
+	return jobqueues[name]
+}
+
+func CloseQueues() {
+	for _, q := range jobqueues {
+		q.Stop()
+	}
+}
diff --git a/go.mod b/go.mod
index 0a118cf..311afb6 100644
--- a/go.mod
+++ b/go.mod
@@ -63,6 +63,7 @@ require (
 	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/mattn/go-isatty v0.0.16 // indirect
 	github.com/mattn/go-sqlite3 v2.0.3+incompatible // indirect
+	github.com/muety/artifex v0.0.0-20221119195407-0ccdcf919cae // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20220927061507-ef77025ab5aa // indirect
 	github.com/robfig/cron/v3 v3.0.1 // indirect
diff --git a/go.sum b/go.sum
index 937577b..a552912 100644
--- a/go.sum
+++ b/go.sum
@@ -179,6 +179,8 @@ github.com/mattn/go-sqlite3 v2.0.3+incompatible h1:gXHsfypPkaMZrKbD5209QV9jbUTJK
 github.com/mattn/go-sqlite3 v2.0.3+incompatible/go.mod h1:FPy6KqzDD04eiIsT53CuJW3U88zkxoIYsOqkbpncsNc=
 github.com/mitchellh/hashstructure/v2 v2.0.2 h1:vGKWl0YJqUNxE8d+h8f6NJLcCJrgbhC4NcD46KavDd4=
 github.com/mitchellh/hashstructure/v2 v2.0.2/go.mod h1:MG3aRVU/N29oo/V/IhBX8GR/zz4kQkprJgF2EVszyDE=
+github.com/muety/artifex v0.0.0-20221119195407-0ccdcf919cae h1:f9HA6uXm/MuI1zqsLTUioA2awahxdHv6LtKH8P9njKM=
+github.com/muety/artifex v0.0.0-20221119195407-0ccdcf919cae/go.mod h1:ohgA8vHxRH0ErHcJejxICnAp49PK/6ZezEJ69zrx0/A=
 github.com/narqo/go-badge v0.0.0-20220127184443-140af28a266e h1:bR8DQ4ZfItytLJwRlrLOPUHd5z18V6tECwYQFy8W+8g=
 github.com/narqo/go-badge v0.0.0-20220127184443-140af28a266e/go.mod h1:m9BzkaxwU4IfPQi9ko23cmuFltayFe8iS0dlRlnEWiM=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e/go.mod h1:zD1mROLANZcx1PVRCS0qkT7pwLkGfwJo4zjcN/Tysno=
diff --git a/services/report.go b/services/report.go
index c332c29..b2d473c 100644
--- a/services/report.go
+++ b/services/report.go
@@ -1,21 +1,20 @@
 package services
 
 import (
+	"github.com/duke-git/lancet/v2/slice"
 	"github.com/emvi/logbuch"
-	"github.com/go-co-op/gocron"
 	"github.com/leandro-lugaresi/hub"
 	"github.com/muety/wakapi/config"
 	"github.com/muety/wakapi/models"
 	"math/rand"
-	"sync"
 	"time"
 )
 
-var reportLock = sync.Mutex{}
+// delay between evey report generation task (to throttle email sending frequency)
+const reportDelay = 15 * time.Second
 
-// range for random offset to add / subtract when scheduling a new job
-// to avoid all mails being sent at once, but distributed over 2*offsetIntervalMin minutes
-const offsetIntervalMin = 15
+// past time range to cover in the report
+const reportRange = 7 * 24 * time.Hour
 
 type ReportService struct {
 	config         *config.Config
@@ -23,7 +22,6 @@ type ReportService struct {
 	summaryService ISummaryService
 	userService    IUserService
 	mailService    IMailService
-	scheduler      *gocron.Scheduler
 	rand           *rand.Rand
 }
 
@@ -34,80 +32,55 @@ func NewReportService(summaryService ISummaryService, userService IUserService,
 		summaryService: summaryService,
 		userService:    userService,
 		mailService:    mailService,
-		scheduler:      gocron.NewScheduler(time.Local),
 		rand:           rand.New(rand.NewSource(time.Now().Unix())),
 	}
 
-	srv.scheduler.StartAsync()
-
-	sub := srv.eventBus.Subscribe(0, config.EventUserUpdate)
-	go func(sub *hub.Subscription) {
-		for m := range sub.Receiver {
-			srv.SyncSchedule(m.Fields[config.FieldPayload].(*models.User))
-		}
-	}(&sub)
-
 	return srv
 }
 
 func (srv *ReportService) Schedule() {
 	logbuch.Info("initializing report service")
 
-	users, err := srv.userService.GetAllByReports(true)
-	if err != nil {
-		config.Log().Fatal("%v", err)
-	}
-
-	logbuch.Info("scheduling reports for %d users", len(users))
-	for _, u := range users {
-		srv.SyncSchedule(u)
-	}
-}
-
-// SyncSchedule syncs the currently active schedulers with the user's wish about whether or not to receive reports.
-// Returns whether a scheduler is active after this operation has run.
-func (srv *ReportService) SyncSchedule(u *models.User) bool {
-	reportLock.Lock()
-	defer reportLock.Unlock()
-
-	// unschedule
-	if !u.ReportsWeekly {
-		_ = srv.scheduler.RemoveByTag(u.ID)
-		logbuch.Info("disabled scheduled reports for user %s", u.ID)
-		return false
-	}
-
-	// schedule
-	if job := srv.getJobByTag(u.ID); job == nil && u.ReportsWeekly {
-		t, _ := time.ParseInLocation("15:04", srv.config.App.GetWeeklyReportTime(), u.TZ())
-		t = t.Add(time.Duration(srv.rand.Intn(offsetIntervalMin*60)) * time.Second)
-		if job, err := srv.scheduler.
-			SingletonMode().
-			Every(1).
-			Week().
-			Weekday(srv.config.App.GetWeeklyReportDay()).
-			At(t).
-			Tag(u.ID).
-			Do(srv.Run, u, 7*24*time.Hour); err != nil {
-			config.Log().Error("failed to schedule report job for user '%s' - %v", u.ID, err)
-		} else {
-			logbuch.Info("next report for user %s is scheduled for %v", u.ID, job.NextRun())
+	_, err := config.GetDefaultQueue().DispatchCron(func() {
+		// fetch all users with reports enabled
+		users, err := srv.userService.GetAllByReports(true)
+		if err != nil {
+			config.Log().Error("failed to get users for report generation, %v", err)
+			return
 		}
-	}
 
-	return u.ReportsWeekly
+		// filter users who have their email set
+		users = slice.Filter[*models.User](users, func(i int, u *models.User) bool {
+			return u.Email != ""
+		})
+
+		// schedule jobs, throttled by one job per 15 seconds
+		logbuch.Info("scheduling report generation for %d users", len(users))
+		for i, u := range users {
+			err := config.GetQueue(config.QueueMails).DispatchIn(func() {
+				if err := srv.SendReport(u, reportRange); err != nil {
+					config.Log().Error("failed to generate report for '%s', %v", u.ID, err)
+				}
+			}, time.Duration(i)*reportDelay)
+
+			if err != nil {
+				config.Log().Error("failed to dispatch report generation job for user '%s', %v", u.ID, err)
+			}
+		}
+	}, srv.config.App.GetWeeklyReportCron())
+
+	if err != nil {
+		config.Log().Error("failed to dispatch report generation jobs, %v", err)
+	}
 }
 
-func (srv *ReportService) Run(user *models.User, duration time.Duration) error {
+func (srv *ReportService) SendReport(user *models.User, duration time.Duration) error {
 	if user.Email == "" {
 		logbuch.Warn("not generating report for '%s' as no e-mail address is set")
 		return nil
 	}
 
-	if !srv.SyncSchedule(user) {
-		logbuch.Info("reports for user '%s' were turned off in the meanwhile since last report job ran")
-		return nil
-	}
+	logbuch.Info("generating report for '%s'", user.ID)
 
 	end := time.Now().In(user.TZ())
 	start := time.Now().Add(-1 * duration)
@@ -126,21 +99,10 @@ func (srv *ReportService) Run(user *models.User, duration time.Duration) error {
 	}
 
 	if err := srv.mailService.SendReport(user, report); err != nil {
-		config.Log().Error("failed to send report for '%s' - %v", user.ID, err)
+		config.Log().Error("failed to send report for '%s', %v", user.ID, err)
 		return err
 	}
 
 	logbuch.Info("sent report to user '%s'", user.ID)
 	return nil
 }
-
-func (srv *ReportService) getJobByTag(tag string) *gocron.Job {
-	for _, j := range srv.scheduler.Jobs() {
-		for _, t := range j.Tags() {
-			if t == tag {
-				return j
-			}
-		}
-	}
-	return nil
-}
diff --git a/services/services.go b/services/services.go
index 867e7bf..4920e30 100644
--- a/services/services.go
+++ b/services/services.go
@@ -93,8 +93,7 @@ type ISummaryService interface {
 
 type IReportService interface {
 	Schedule()
-	SyncSchedule(user *models.User) bool
-	Run(*models.User, time.Duration) error
+	SendReport(*models.User, time.Duration) error
 }
 
 type ILeaderboardService interface {
diff --git a/utils/cron.go b/utils/cron.go
new file mode 100644
index 0000000..d2444f3
--- /dev/null
+++ b/utils/cron.go
@@ -0,0 +1,11 @@
+package utils
+
+import "strings"
+
+func CronPadToSecondly(expr string) string {
+	parts := strings.Split(expr, " ")
+	if len(parts) == 6 {
+		return expr
+	}
+	return "0 " + expr
+}