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SMTP(1) General Commands Manual SMTP(1)

smtpSimple Mail Transfer Protocol client

smtp [-Chnv] [-a authfile] [-F from] [-H helo] [-s server] [-T params] [recipient ...]

The smtp utility is a Simple Mail Transfer Protocol (SMTP) client which can be used to run an SMTP transaction against an SMTP server.

By default, smtp reads the mail content from the standard input, establishes an SMTP session, and runs an SMTP transaction for all the specified recipients. The content is sent unaltered as mail data.

The options are as follows:

Perform a login before sending the message. The username and password are read from authfile and need to be on the first and second line respectively. This option requires a TLS or STARTTLS server.
Do not require server certificate to be valid. This flag is deprecated. Use “-T noverify” instead.
Set the return-path (MAIL FROM) for the SMTP transaction. Default to the current username.
Define the hostname to advertise (HELO) when establishing the SMTP session.
Display usage.
Do not actually execute a transaction, just try to establish an SMTP session and quit. When this option is given, no message is read from the standard input.
Specify the server to connect to and connection parameters. The format is [proto://[user:pass@]]host[:port]. The following protocols are available:

Normal SMTP session with opportunistic STARTTLS.
Normal SMTP session with mandatory STARTTLS.
Plain text SMTP session without TLS.
LMTP session with opportunistic STARTTLS.
LMTP session with mandatory STARTTLS.
Plain text LMTP session without TLS.
SMTP session with forced TLS on connection.

Defaults to “smtp://localhost:25”.

Set specific parameters for TLS sessions. The params string is a comma or space separated list of options. The available options are:
Use filename as root certificates file instead of the system default.
Specify the allowed ciphers. Refer to tls_config_set_ciphers(3) for value.
Disable Server Name Indication (SNI).
Do not require server certificate to be valid.
Specify the protocols to use. Refer to tls_config_parse_protocols(3) for value.
Use value for Server Name Indication (SNI). Defaults to the specified server hostname.
Be more verbose. This option can be specified multiple times.


The smtp program first appeared in OpenBSD 6.4.

May 23, 2021 OpenBSD-current