diff --git a/manager_builder.go b/manager_builder.go
index c782751..0ed30d5 100644
--- a/manager_builder.go
+++ b/manager_builder.go
@@ -15,11 +15,16 @@ const (
 	// DefaultAppVersion is the default app version used to communicate with the API.
 	// This must be changed (using the WithAppVersion option) for production use.
 	DefaultAppVersion = "go-proton-api"
+
+	// DefaultUserAgent is the default user agent used to communicate with the API.
+	// See: https://github.com/emersion/hydroxide/issues/252
+	DefaultUserAgent = ""
 )
 
 type managerBuilder struct {
 	hostURL      string
 	appVersion   string
+	userAgent    string
 	transport    http.RoundTripper
 	verifyProofs bool
 	cookieJar    http.CookieJar
@@ -33,6 +38,7 @@ func newManagerBuilder() *managerBuilder {
 	return &managerBuilder{
 		hostURL:      DefaultHostURL,
 		appVersion:   DefaultAppVersion,
+		userAgent:    DefaultUserAgent,
 		transport:    http.DefaultTransport,
 		verifyProofs: true,
 		cookieJar:    nil,
@@ -74,6 +80,7 @@ func (builder *managerBuilder) build() *Manager {
 	// Set app version in header.
 	m.rc.OnBeforeRequest(func(_ *resty.Client, req *resty.Request) error {
 		req.SetHeader("x-pm-appversion", builder.appVersion)
+		req.SetHeader("User-Agent", builder.userAgent)
 		return nil
 	})
 
diff --git a/option.go b/option.go
index 281d469..5dc3239 100644
--- a/option.go
+++ b/option.go
@@ -32,6 +32,20 @@ func WithAppVersion(appVersion string) Option {
 	}
 }
 
+type withUserAgent struct {
+	userAgent string
+}
+
+func (opt withUserAgent) config(builder *managerBuilder) {
+	builder.userAgent = opt.userAgent
+}
+
+func WithUserAgent(userAgent string) Option {
+	return &withUserAgent{
+		userAgent: userAgent,
+	}
+}
+
 type withAppVersion struct {
 	appVersion string
 }