diff --git a/internal/user/smtp.go b/internal/user/smtp.go
index c16d2d27..09080e54 100644
--- a/internal/user/smtp.go
+++ b/internal/user/smtp.go
@@ -23,6 +23,7 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
+	"mime"
 	"net/mail"
 	"runtime"
 	"strings"
@@ -419,7 +420,7 @@ func createAttachments(
 		attachment, err := client.UploadAttachment(ctx, addrKR, proton.CreateAttachmentReq{
 			Filename:    att.Name,
 			MessageID:   draftID,
-			MIMEType:    rfc822.MIMEType(att.MIMEType),
+			MIMEType:    rfc822.MIMEType(mime.FormatMediaType(att.MIMEType, att.MIMEParams)),
 			Disposition: att.Disposition,
 			ContentID:   att.ContentID,
 			Body:        att.Data,
diff --git a/pkg/message/parser.go b/pkg/message/parser.go
index e0aa9445..6d5ee23c 100644
--- a/pkg/message/parser.go
+++ b/pkg/message/parser.go
@@ -66,6 +66,7 @@ type Attachment struct {
 	Name        string
 	ContentID   string
 	MIMEType    string
+	MIMEParams  map[string]string
 	Disposition proton.Disposition
 	Data        []byte
 }
@@ -523,6 +524,7 @@ func parseAttachment(h message.Header, body []byte) (Attachment, error) {
 		return Attachment{}, err
 	}
 	att.MIMEType = mimeType
+	att.MIMEParams = mimeTypeParams
 
 	// Prefer attachment name from filename param in content disposition.
 	// If not available, try to get it from name param in content type.