esmtp การใช้

• Following the lead of ESMTP ( RFC 5321 ), capabilities beginning with an X signify local capabilities.
• In the simplest case, an ESMTP server will declare a maximum SIZE immediately after receiving an EHLO.
• DSNs can be explicitly solicited with an SMTP Service Extension ( ESMTP ), however it is not widely used.
• Modern clients may use the ESMTP extension keyword SIZE to query the server for the maximum message size that will be accepted.
• The ESMTP format was restated in RFC 2821 ( superseding RFC 821 ) and updated to the latest definition in RFC 5321 in 2008.
• This is no longer such a problem since most e-mail servers today use ESMTP, and hence 8-bit characters are acceptable.
• An ESMTP server returns the code 250 OK in a multi-line reply with its domain and a list of keywords to indicate supported extensions.
• A RFC 821 compliant server returns error code 500, allowing ESMTP clients to try either " HELO " or " QUIT ".
• The main identification feature for ESMTP clients is to open a transmission with the command " EHLO " ( Extended HELLO ), rather than " HELO " ( Hello, the original RFC 821 standard ).
• Sendmail supports a variety of mail transfer protocols, including SMTP, ESMTP, DECnet's Mail-11, HylaFax, QuickPage and UUCP . Additionally, Sendmail v8.12 introduced support for milters-external mail filtering programs that can participate in each step of the SMTP conversation.