diff --git a/connector/microsoft/microsoft.go b/connector/microsoft/microsoft.go
index 33034cc5..3a3cf3b5 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"`
+	EmailToLowercase     bool            `json:"emailToLowercase"`
 }
 
 // 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,
+		emailToLowercase:     c.EmailToLowercase,
 	}
 	// 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
+	emailToLowercase     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.emailToLowercase {
+		user.Email = strings.ToLower(user.Email)
+	}
+
 	identity = connector.Identity{
 		UserID:        user.ID,
 		Username:      user.Name,