I am trying to scan inbound emails that are fetched by Thunderbird, the iOS mail client, and the Gmail Android app. Sending and receiving seems to work, however, copying to the sent folder does not, unless I accept invalid certificates under the POP/IMAP TLS configuration. The problem does not arise on accounts that use STARTTLS. Only on SSL/TLS accounts. The Sophos XG CA certificate is added as a trusted source on the client side. I have the following settings on the firewall active:
- Firewall rule:
- Source: Any, Any
- Destination: Any, Any, [IMAP(S), POP3(S)]
- Web policy active
- Block QUIC protocol
- Scan HTTP and decrypted HTTPS, Use zero-day-protection, scan FTP
- Block high risk apps
- IPS: lantowan_general
- scan email content: POP3(S), IMAP(S)
- NAT:
- linked to this firewall rule
- SSL/TLS Inspection
- decrypt, maximum compatibility profile
- Email policy
- dual av scanning
- Mail, General Settings; POP and IMAP TLS configuration:
- TLS Certificate: the default Sophos CA cert
- disable legacy TLS
- allow invalid certificate
What am I missing? Why do I need to allow invalid certificates in order to copy emails to the sent folder?
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