Configure SMTP output

Setting	Default	Effect
Host / port / authentication	Base values	SMTP endpoint and identity. Configure the server's required port/TLS/auth path explicitly.
To / CC / BCC	Empty	Tag-processed recipients. Validate resolved addresses and prevent untrusted recipient injection.
Subject	Empty	Tag-processed subject. Keep secrets/business-sensitive data out of subject lines.
Text / HTML body	Empty	Message bodies. Escape/validate data inserted into HTML.
Load attachment into text body	Cleared	Uses attachment content as text body. Test encoding/size and data disclosure.
Load attachment into HTML body	Cleared	Uses attachment content as HTML body. Treat attachment content as untrusted.
Read receipt	Cleared	Requests a receipt; it is not proof that the recipient read or processed the business message.

Test exact resolved recipients, empty/large/multiple/binary attachments, non-ASCII subject/body, SMTP acceptance/rejection, ambiguous timeout and duplicate sends. SMTP acceptance is not recipient inbox or business-processing confirmation. Before retrying, correlate Transport log, message identity and mail-system evidence. Protect trace logs because SMTP/auth/message content can be sensitive.