conform to pEp standards

gpgmymail

@@ -42,6 +42,7 @@ import gnupg
 
 # constants
 DEFAULT_ENCODING='utf-8'  # default is latin-1 which fails w some unicode chars
+PEP_SUBJECT='=?utf-8?Q?p=E2=89=A1p?='
 
 def is_message_encrypted(message: email.message.Message) -> bool:
     """Determines whether or not an email message is encrypted.
@@ -169,6 +170,27 @@ def decode_email(message: email.message.Message) -> email.message.Message:
     
     return decoded_bytes_to_return_value(decoded_bytes)
 
+def set_email_header(
+    message: email.message.Message,
+    name: str,
+    value: str
+) -> None:
+    """
+    Set the header of an email Message. Will either replace the first instance
+    of the header, or if the header is not present, will add the header.
+
+    Note: Python passes objects as references, so there is no need for a return
+    value.
+
+    :param message: the Message object to be modified
+    :param name: the email header to set
+    :param value: the value to set the header to
+    """
+    if message.get(name):
+        message.replace_header(name, value)
+    else:
+        message.add_header(name, value)
+
 def encrypt(
         message: email.message.Message,
         recipients: typing.List[str],
@@ -254,6 +276,10 @@ def encrypt(
         if key.lower() not in headers_not_to_override:
             encmsg[key] = value
 
+    # mark as confirming to pEp: https://blog.jak-linux.org/2019/06/13/encrypted-email-storage/#pretty-easy-privacy-pp
+    set_email_header(encmsg, 'Subject', PEP_SUBJECT)
+    set_email_header(encmsg, 'X-pEp-Version', '2.1')
+
     return encmsg.as_string()
 
 def decrypt(message: email.message.Message, *, encoding: str = DEFAULT_ENCODING) -> str: