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RFC 2821 (rfc2821) - Simple Mail Transfer Protocol (Site not responding. Last check: 2007-10-21) |
 | | SMTP clients that transfer all traffic, regardless of the target domain names associated with the individual messages, or that do not maintain queues for retrying message transmissions that initially cannot be completed, may otherwise conform to this specification but are not considered fully-capable. |
 | | SMTP server implementations that support the 251 and/or 551 reply codes are strongly encouraged to provide configuration mechanisms so that sites which conclude that they would undesirably disclose information can disable or restrict their use. |
 | | SMTP clients that experience a connection close, reset, or other communications failure due to circumstances not under their control (in violation of the intent of this specification but sometimes unavoidable) SHOULD, to maintain the robustness of the mail system, treat the mail transaction as if a 451 response had been received and act accordingly. |
| www.faqs.org /rfcs/rfc2821.html (18604 words) |