Add info about how to re-enable TLS 1.0 and 1.1

docs/u_e-reeanble-weak-protocols.md

@@ -0,0 +1,26 @@
+On February the 12th 2020 we disabled the deprecated protocols TLS 1.0 and 1.1.
+
+Unauthenticated mail via SMTP on port 25/tcp does still accept >= TLS 1.0 . It is better to accept a weak encryption than none at all.
+
+**How to re-enable weak protocols?**
+
+Edit `data/conf/postfix/extra.cf`:
+
+```
+submission_smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
+smtps_smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
+```
+
+Edit `data/conf/dovecot/extra.conf`:
+
+```
+ssl_min_protocol = TLSv1
+```
+
+Restart the affected services:
+
+```
+docker-compose restart postfix-mailcow dovecot-mailcow
+```
+
+Hint: You can enable TLS 1.2 in Windows 7.

mkdocs.yml

@@ -95,6 +95,7 @@ nav:
   - 'Redirect HTTP to HTTPS': 'u_e-80_to_443.md'
   - 'Adjust Service Configurations': 'u_e-change_config.md'
   - 'Deinstall': 'u_e-deinstall.md'
+  - 'Re-enable TLS 1.0 upwards': 'u_e-reeanble-weak-protocols.md'
 - 'Client Configuration':
   - 'Overview': 'client.md'
   - 'Android': 'client/client-android.md'