Fixed encoding issue on Python 3 for some mail servers. [master] (#1607)

Fixed encoding issue on Python 3 for some mail servers.

This could result in missing characters in an email body.
See plone/Products.CMFPlone#3754

Co-authored-by: Timo Stollenwerk <tisto@users.noreply.github.com>

news/3754.bugfix

@@ -0,0 +1,3 @@
+Fixed encoding issue on Python 3 for some mail servers.
+This could result in missing characters in an email body.
+[maurits]

src/plone/restapi/services/email_send/post.py

@@ -1,6 +1,5 @@
 from AccessControl import getSecurityManager
 from AccessControl.Permissions import use_mailhost_services
-from email.mime.text import MIMEText
 from plone.registry.interfaces import IRegistry
 from plone.restapi import _
 from plone.restapi.bbb import IMailSchema
@@ -15,6 +14,14 @@
 
 import plone
 
+try:
+    # Products.MailHost has a patch to fix quoted-printable soft line breaks.
+    # See https://github.com/zopefoundation/Products.MailHost/issues/35
+    from Products.MailHost.MailHost import message_from_string
+except ImportError:
+    # If the patch is ever removed, we fall back to the standard library.
+    from email import message_from_string
+
 
 class EmailSendPost(Service):
     def reply(self):
@@ -99,7 +106,7 @@ def reply(self):
 
         message = f"{message_intro} \n {message}"
 
-        message = MIMEText(message, "plain", encoding)
+        message = message_from_string(message)
         message["Reply-To"] = sender_from_address
         try:
             host.send(