Merge commit from fork

With [smtp] ssl = False (the default) or [imap] ssl = False, mailsuite
upgraded the connection only if the server's plain-text EHLO/CAPABILITY
reply advertised STARTTLS, and otherwise authenticated in plain text. An
on-path attacker who stripped STARTTLS received the credentials and the
emailed results (CWE-319).

- Require mailsuite >= 2.3.4 (GHSA-2x4j-7g3q-wr6f), whose default
  refuses to authenticate over a connection that was not upgraded.
- Add [imap] and [smtp] starttls (unset = require STARTTLS; false =
  explicit plain-text opt-out, for loopback servers such as DavMail),
  with a startup warning when the opt-out is set and ssl is False.
- Add a starttls argument to email_results().
- Document both options; set starttls = False in the DavMail example.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

pyproject.toml

@@ -59,7 +59,7 @@ dependencies = [
     # No extras: the base mailsuite supplies IMAP and Maildir connections
     # plus mail-parser. Gmail and Microsoft Graph come from the gmail and
     # msgraph extras below.
-    "mailsuite>=2.3.3",
+    "mailsuite>=2.3.4",
     "maxminddb>=2.0.0",
     "publicsuffixlist>=0.10.0",
     # Imported directly at utils.py:39 (dateutil.parser). It used to
@@ -96,13 +96,13 @@ loganalytics = [
     "azure-monitor-ingestion>=1.0.0",
 ]
 msgraph = [
-    "mailsuite[msgraph]>=2.3.3",
+    "mailsuite[msgraph]>=2.3.4",
     # Imported directly in cli.py for Graph error handling; otherwise
     # only a transitive dep of mailsuite[msgraph] -> msgraph-sdk.
     "microsoft-kiota-abstractions>=1.8.0",
 ]
 gmail = [
-    "mailsuite[gmail]>=2.3.3",
+    "mailsuite[gmail]>=2.3.4",
 ]
 # `all` must stay the union of every extra above — and must keep
 # excluding `postgresql`: psycopg's prebuilt binary wheels do not exist
@@ -118,7 +118,7 @@ all = [
     "boto3>=1.16.63",
     "elasticsearch>=8.18,<9",
     "kafka-python>=2.3.2",
-    "mailsuite[gmail,msgraph]>=2.3.3",
+    "mailsuite[gmail,msgraph]>=2.3.4",
     "microsoft-kiota-abstractions>=1.8.0",
     "opensearch-py>=2.4.2,<=4.0.0",
     "pygelf>=0.4.2",