diff --git a/connector/microsoft/microsoft.go b/connector/microsoft/microsoft.go
index ff27182d..0d823270 100644
--- a/connector/microsoft/microsoft.go
+++ b/connector/microsoft/microsoft.go
@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
 	"sync"
 	"time"
 
@@ -51,6 +52,7 @@ type Config struct {
 	Groups               []string        `json:"groups"`
 	GroupNameFormat      GroupNameFormat `json:"groupNameFormat"`
 	UseGroupsAsWhitelist bool            `json:"useGroupsAsWhitelist"`
+	UpnToLowercase       bool            `json:"upnToLowercase"`
 }
 
 // Open returns a strategy for logging in through Microsoft.
@@ -67,6 +69,7 @@ func (c *Config) Open(id string, logger log.Logger) (connector.Connector, error)
 		groupNameFormat:      c.GroupNameFormat,
 		useGroupsAsWhitelist: c.UseGroupsAsWhitelist,
 		logger:               logger,
+		upnToLowercase:       c.UpnToLowercase,
 	}
 	// By default allow logins from both personal and business/school
 	// accounts.
@@ -109,6 +112,7 @@ type microsoftConnector struct {
 	groups               []string
 	useGroupsAsWhitelist bool
 	logger               log.Logger
+	upnToLowercase       bool
 }
 
 func (c *microsoftConnector) isOrgTenant() bool {
@@ -171,6 +175,10 @@ func (c *microsoftConnector) HandleCallback(s connector.Scopes, r *http.Request)
 		return identity, fmt.Errorf("microsoft: get user: %v", err)
 	}
 
+	if c.upnToLowercase {
+		user.Email = strings.ToLower(user.Email)
+	}
+
 	identity = connector.Identity{
 		UserID:        user.ID,
 		Username:      user.Name,
diff --git a/go.mod b/go.mod
index 86a1e9c8..69457b3b 100644
--- a/go.mod
+++ b/go.mod
@@ -25,6 +25,7 @@ require (
 	github.com/lib/pq v1.3.0
 	github.com/mattermost/xml-roundtrip-validator v0.0.0-20201204154048-1a8688af4cf1
 	github.com/mattn/go-sqlite3 v1.11.0
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/pkg/errors v0.9.1
 	github.com/pquerna/cachecontrol v0.0.0-20180517163645-1555304b9b35 // indirect
 	github.com/prometheus/client_golang v1.4.0
@@ -46,6 +47,7 @@ require (
 	gopkg.in/asn1-ber.v1 v1.0.0-20181015200546-f715ec2f112d // indirect
 	gopkg.in/ldap.v2 v2.5.1
 	gopkg.in/square/go-jose.v2 v2.4.1
+	honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc // indirect
 	sigs.k8s.io/testing_frameworks v0.1.2
 )