C:\>curl --version
curl 8.16.0 (Windows) libcurl/8.16.0 Schannel zlib/1.3.1 WinIDN
Release-Date: 2025-09-10
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns ldap ldaps mqtt pop3 pop3s smb smbs smtp smtps telnet tftp ws wss
Features: alt-svc AsynchDNS HSTS HTTPS-proxy IDN IPv6 Kerberos Largefile libz NTLM SPNEGO SSL SSPI threadsafe Unicode UnixSockets

C:\>curl --url smtp://smtp.acme.com:587 --mail-from test@acme.com --mail-rcpt test@acme.com --upload-file test.txt -v --negotiate -u :
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0* Host smtp.acme.com:587 was resolved.
* IPv6: (none)
* IPv4: 192.181.0.52
*   Trying 192.181.0.52:587...
* Established connection to smtp.acme.com (192.181.0.52 port 587) from 192.181.0.50 port 62182
< 220 smtp.acme.com Microsoft ESMTP MAIL Service ready at Tue, 12 May 2026 06:38:58 -0700
> EHLO test.txt
< 250-smtp.acme.com Hello [192.181.0.50]
< 250-SIZE 37748736
< 250-PIPELINING
< 250-DSN
< 250-ENHANCEDSTATUSCODES
< 250-STARTTLS
< 250-AUTH GSSAPI NTLM
< 250-8BITMIME
< 250-BINARYMIME
< 250-CHUNKING
< 250 SMTPUTF8
> AUTH GSSAPI
< 334 GSSAPI supported
> YIIHEgYJ.....lIOM=
< 334 BQQB/......ALuA=
> BQQA/wAMAAwA.....lU1SisnOAEAAAA=
< 235 2.7.0 Authentication successful
> MAIL FROM:<test@acme.com> SIZE=164
< 250 2.1.0 Sender OK
> RCPT TO:<test@acme.com>
< 250 2.1.5 Recipient OK
> DATA
< 354 Start mail input; end with <CRLF>.<CRLF>
} [169 bytes data]
* upload completely sent off: 169 bytes
< 250 2.6.0 <89790372-df18-4846-81d2-8fad4619e085@smtp.acme.com> [InternalId=708669603843, Hostname=smtp.acme.com] 1365 bytes in 0.115, 11.585 KB/sec Queued mail for delivery
103   164    0     0  103   169      0    286 --:--:-- --:--:-- --:--:--   290
* Connection #0 to host smtp.acme.com:587 left intact