| SMTP_HOST | Yes | Hostname of the SMTP server, e.g. smtp.example.net. |
| SMTP_PORT | No | Port. Defaults to 587 for starttls, 465 for implicit, 25 for none. |
| SMTP_TLS | No | starttls (default), implicit or none. STARTTLS is required, never opportunistic. |
| SMTP_USER | Yes | Username for SMTP authentication. |
| SMTP_PASSWORD | Yes | Password or app-specific password for SMTP authentication. Secret. |
| SMTP_FROM | Yes | The only sender this server will use, e.g. "Name <person@example.net>". There is no from parameter. |
| SMTP_REPLY_TO | No | Reply-To header on every message, e.g. "Team <team@example.net>". Unset means no Reply-To header and replies go to SMTP_FROM. There is no reply_to parameter. |
| SMTP_ALLOW_SEND | No | Set to "true" to register the sending tools. Defaults to false: the server cannot send until it is set. |
| SMTP_ALLOWED_RECIPIENTS | No | Comma-separated addresses and @domains this server may write to. Required with SMTP_ALLOW_SEND=true; "*" allows any. |
| SMTP_MAX_RECIPIENTS | No | Maximum distinct recipients across To, Cc and Bcc in one message. Default 10. |
| SMTP_MAX_SENDS_PER_HOUR | No | Sliding hourly cap on messages sent. Default 20. |
| SMTP_MAX_MESSAGE_BYTES | No | Maximum size of the composed message. Default 10485760. |
| SMTP_MAX_ATTACHMENT_BYTES | No | Maximum size of a single attachment. Default 5242880. |
| SMTP_ATTACHMENT_DIR | No | Directory attachments are read from. Unset means attachments are unavailable. |
| SMTP_ATTACHMENT_TYPES | No | Comma-separated content types that may be attached. Defaults to a document and image allowlist. |
| SMTP_SIGNATURE | No | Text appended below the standard signature delimiter of every message. |
| SMTP_AUDIT_LOG | No | File the audit lines are appended to, in addition to stderr. |
| SMTP_ALLOW_TOOLS | No | Comma-separated tool names, a prefix with one trailing *, or "essential" for the curated preset. |
| SMTP_DENY_TOOLS | No | Comma-separated tool names or prefixes to remove, applied after SMTP_ALLOW_TOOLS. |
| SMTP_INSECURE_TLS | No | Set to "true" to accept self-signed certificates. Prefer a proper internal CA. |
| SMTP_HOST | Yes | Hostname of the SMTP server, e.g. smtp.example.net. |
| SMTP_PORT | No | Port. Defaults to 587 for starttls, 465 for implicit, 25 for none. |
| SMTP_TLS | No | starttls (default), implicit or none. STARTTLS is required, never opportunistic. |
| SMTP_USER | Yes | Username for SMTP authentication. |
| SMTP_PASSWORD | Yes | Password or app-specific password for SMTP authentication. Secret. |
| SMTP_FROM | Yes | The only sender this server will use, e.g. "Name <person@example.net>". There is no from parameter. |
| SMTP_REPLY_TO | No | Reply-To header on every message, e.g. "Team <team@example.net>". Unset means no Reply-To header and replies go to SMTP_FROM. There is no reply_to parameter. |
| SMTP_ALLOW_SEND | No | Set to "true" to register the sending tools. Defaults to false: the server cannot send until it is set. |
| SMTP_ALLOWED_RECIPIENTS | No | Comma-separated addresses and @domains this server may write to. Required with SMTP_ALLOW_SEND=true; "*" allows any. |
| SMTP_MAX_RECIPIENTS | No | Maximum distinct recipients across To, Cc and Bcc in one message. Default 10. |
| SMTP_MAX_SENDS_PER_HOUR | No | Sliding hourly cap on messages sent. Default 20. |
| SMTP_MAX_MESSAGE_BYTES | No | Maximum size of the composed message. Default 10485760. |
| SMTP_MAX_ATTACHMENT_BYTES | No | Maximum size of a single attachment. Default 5242880. |
| SMTP_ATTACHMENT_DIR | No | Directory attachments are read from. Unset means attachments are unavailable. |
| SMTP_ATTACHMENT_TYPES | No | Comma-separated content types that may be attached. Defaults to a document and image allowlist. |
| SMTP_SIGNATURE | No | Text appended below the standard signature delimiter of every message. |
| SMTP_AUDIT_LOG | No | File the audit lines are appended to, in addition to stderr. |
| SMTP_ALLOW_TOOLS | No | Comma-separated tool names, a prefix with one trailing *, or "essential" for the curated preset. |
| SMTP_DENY_TOOLS | No | Comma-separated tool names or prefixes to remove, applied after SMTP_ALLOW_TOOLS. |
| SMTP_INSECURE_TLS | No | Set to "true" to accept self-signed certificates. Prefer a proper internal CA. |