SMTP protocol settings
The protocol settings control the behaviour when receiving emails, the SMTP timeouts and the SMTP status messages.
Behaviour tab
Application of rules
If an email is sent to multiple recipients, different rules may apply to the email. NoSpamProxy can force the sending system to send a separate email for each individual recipient. This setting prevents conflicts caused by emails sent to multiple recipients, e.g. if an email is sent to two recipients via one connection and two different rules would apply.
NOTE: By using SMTP, it is not possible to provide independent feedback for individual recipients. Only the entire connection can be terminated.
Treat all recipients with the same rule as the first recipient The rule that applies to the first recipient is applied to all recipients of this email.
Temporarily reject all recipients that do not match the rule of the first recipient All recipients that do not match the rule of the first recipient are temporarily rejected. NoSpamProxy sends the error message Too many recipientsto the inbound system. A new delivery attempt will be made for the rejected emails. This allows NoSpamProxy to apply the appropriate rule for each recipient. However, the emails are delivered multiple times by the sender.
NOTE: This function allows you to control the email assessment. Disadvantages are multiple transmissions and not fully RFC-compliant behavior.
Duplicate email detection
NoSpamProxy recognises if the same email is received multiple times. Sending the same email repeatedly usually occurs due to incorrect configuration such as email loops. You can set whether these emails should be discarded or not, as well as the time frame for the detection.
Do not check for duplicate emails There is no check for duplicate emails.
Silently discard duplicate emails Duplicate emails received within the configured time period are silently discarded.
Validation timeout handling
You can determine how emails whose validation time exceeds the maximum values configured under Protocol timeouts are handled.
Accept emails E-mails whose validation time exceeds the maximum values are accepted.
Temporarily reject emails Emails whose validation time exceeds the maximum values are temporarily rejected.
NOTE: If the malware scan is not completed when a validation timeout occurs, the respective email will always be temporarily rejected.
NOTE: Emails are rejected in any case if they were previously rejected temporarily or permanently by an action.
Protocol timeouts tab
NOTE: Adjusting the timeouts has a major impact on the resource requirements of your server during heavy email traffic.
In the SMTP protocol timeout settings section you can specify when NoSpamProxy disconnects in case of no activity. This is configured for two sections within the SMTP protocol.
Envelope timeout Defines the timeout for the commands within the so-called envelope. This affects all commands up to the DATA command (HELO/EHLO, MAIL FROM, RCPT TO).
Body timeout As soon as the DATA command has been sent, the setting under Body timeoutapplies.
NOTE: It makes sense to separate the timeouts, since timeouts can occur more frequently than with the envelope when the body part is transferred by means of filters and actions connected in between. This is transmitted very promptly and smoothly during a normal transmission. A longer waiting time in this part of the email transfer rather indicates a DoS attack or similar. Therefore you have the possibility to reduce the timeout of the envelope part in case of emergency.
Status messages tab
The status messages determine which texts (SMTP strings) NoSpamProxy sends to other servers. The SMTP replies are standard specifications in the SMTP handshake, which are usually not visible to the normal user. Nevertheless, it may be useful to change the information as required. This can assist administrators with troubleshooting and analysis.
The messages Rejected emails and Blacklisted address are for example important information for the sender of a blocked email.
- To change a message, click in the corresponding input field and change the text.
NOTE: You must not use umlauts for SMTP messages. Umlauts are not supported by the SMTP protocol used.